design, manufacture, and installation of concrete piles

mm ρs = ratio of volume of spiral reinforcement to total vol-ume of core out-to-out of spiral φ = strength reduction factor φc = strength reduction factor in compression φt = strength re

ACI 543R-00 supersedes ACI 543R-74 and became effective January 10, 2000 Copyright  2000, American Concrete Institute.

All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduc- tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.

ACI Committee Reports, Guides, Standard Practices,

and Commentaries are intended for guidance in planning,

designing, executing, and inspecting construction This

document is intended for the use of individuals who are

competent to evaluate the significance and limitations of

its content and recommendations and who will accept

re-sponsibility for the application of the material it contains

The American Concrete Institute disclaims any and all

re-sponsibility for the stated principles The Institute shall

not be liable for any loss or damage arising therefrom

Reference to this document shall not be made in

con-tract documents If items found in this document are

de-sired by the Architect/Engineer to be a part of the contract

documents, they shall be restated in mandatory language

for incorporation by the Architect/Engineer

543R-1

Design, Manufacture, and Installation of

Concrete Piles

ACI 543R-00

This report presents recommendations to assist the design

architect/engi-neer, manufacturer, field engiarchitect/engi-neer, and contractor in the design and use of

most types of concrete piles for many kinds of construction projects The

introductory chapter gives descriptions of the various types of piles and

definitions used in this report.

Chapter 2 discusses factors that should be considered in the design of

piles and pile foundations and presents data to assist the engineer in

evalu-ating and providing for factors that affect the load-carrying capacities of

different types of concrete piles.

Chapter 3 lists the various materials used in constructing concrete piles

and makes recommendations regarding how these materials affect the

qual-ity and strength of concrete Reference is made to applicable codes and

specifications Minimum requirements and basic manufacturing procedures

for precast piles are stated so that design requirements for quality, strength,

and durability can be achieved (Chapter 4) The concluding Chapter 5

out-lines general principles for proper installation of piling so that the

struc-tural integrity and ultimate purpose of the pile are achieved Traditional

installation methods, as well as recently developed techniques, are discussed.

Keywords: augered piles; bearing capacity; composite construction

(con-crete and steel); con(con-crete piles; corrosion; drilled piles; foundations; harbor

structures; loads (forces); prestressed concrete; quality control; reinforcing

steels; soil mechanics; storage; tolerances.

CONTENTS

Chapter 1—Introduction, p 543R-2

1.0—General1.1—Types of piles

Chapter 2—Design, p 543R-4

2.0—Notation2.1—General design considerations2.2—Loads and stresses to be resisted2.3—Structural strength design and allowable service capacities

2.4—Installation and service conditions affecting design2.5—Other design and specification considerations

Chapter 3—Materials, p 543R-24

3.1—Concrete3.2—Reinforcement and prestressing materials3.3—Steel casing

3.4—Structural steel cores and stubs3.5—Grout

3.6—Anchorages3.7—Splices

Chapter 4—Manufacture of precast concrete piles,

p 543R-27

4.1—General4.2—Forms4.3—Placement of steel reinforcement4.4—Embedded items

4.5—Mixing, transporting, placing, and curing concrete4.6—Pile manufacturing

4.7—Handling and storage

Reported by ACI Committee 543

Ernest V Acree, Jr James S Graham W T McCalla Roy M Armstrong Mohamad Hussein Stanley Merjan Herbert A Brauner John S Karpinski Clifford R Ohlwiler Robert N Bruce, Jr John B Kelley Jerry A Steding Judith A Costello Viswanath K Kumar John A Tanner

M T Davisson Hugh S Lacy Edward J Ulrich, Jr.

Jorge L Fuentes Chairman

William L Gamble Secretary

Chapter 5—Installation of driven piles, p 543R-31

5.0—Purpose and scope

5.1—Installation equipment, techniques, and methods

5.2—Prevention of damage to piling during installation

5.3—Handling and positioning during installation

5.4—Reinforcing steel and steel core placement

5.5—Concrete placement for CIP and CIS piles

5.6—Pile details

5.7—Extraction of concrete piles

5.8—Concrete sheet piles

Piles are slender structural elements installed in the ground

to support a load or compact the soil They are made of

sev-eral materials or combinations of materials and are installed

by impact driving, jacking, vibrating, jetting, drilling,

grout-ing, or combinations of these techniques Piles are difficult to

summarize and classify because there are many types of

piles, and new types are still being developed The following

discussion deals with only the types of piles currently used in

North American construction projects

Piles can be described by the predominant material from

which they are made: steel; concrete (or cement and other

materials); or timber Composite piles have an upper section

of one material and a lower section of another Piles made

en-tirely of steel are usually H-sections or unfilled pipe;

howev-er, other steel members can be used Timber piles are

typically tree trunks that are peeled, sorted to size, and driven

into place The timber is usually treated with preservatives

but can be used untreated when the pile is positioned entirely

below the permanent water table The design of steel and

timber piles is not considered herein except when they are

used in conjunction with concrete Most of the remaining

types of existing piles contain concrete or a cement-based

material

Driven piles are typically top-driven with an impact

ham-mer activated by air, steam, hydraulic, or diesel mechanisms,

although vibratory drivers are occasionally used Some piles,

such as steel corrugated shells and thin-wall pipe piles,

would be destroyed if top-driven For such piles, an internal

steel mandrel is inserted into the pile to receive the blows of

the hammer and support the shell during installation The pile

is driven into the ground with the mandrel, which is then

withdrawn Driven piles tend to compact the soil beneath the

pile tip

Several types of piles are installed by drilling or rotating

with downward pressure, instead of driving Drilled piles

usually involve concrete or grout placement in direct contact

with the soil, which can produce side-friction resistance

greater than that observed for driven piles On the other hand,

because they are drilled rather than driven, drilled piles do

not compact the soil beneath the pile tip, and in fact, can

loos-en the soil at the tip Postgrouting may be used after tion to densify the soil under the pile tip

installa-Concrete piles can also be classified according to the dition under which the concrete is cast Some concrete piles(precast piles) are cast in a plant before driving, which allowscontrolled inspection of all phases of manufacture Otherpiles are cast-in-place (CIP), a term used in this report to des-ignate piles made of concrete placed into a previously driv-

con-en, enclosed container; concrete-filled corrugated shells andclosed-end pipe are examples of CIP piles Other piles arecast-in-situ (CIS), a term used in this report to designate con-crete cast directly against the earth; drilled piers and auger-grout piles are examples of CIS piles

1.1—Types of piles

1.1.1 Precast concrete piles—This general classification

covers both conventionally reinforced concrete piles andprestressed concrete piles Both types can be formed by cast-ing, spinning (centrifugal casting), slipforming, or extrusionand are made in various cross-sectional shapes, such as trian-gular, square, octagonal, and round Some piles are cast with

a hollow core Precast piles usually have a uniform cross tion but can have a tapered tip Precast concrete piles must bedesigned and manufactured to withstand handling and driv-ing stresses in addition to service loads

sec-1.1.1.1 Reinforced concrete piles—These piles are

constructed of conventionally reinforced concrete with nal reinforcement consisting of a cage made up of severallongitudinal steel bars and lateral steel in the form of individ-ual ties or a spiral

inter-1.1.1.2 Prestressed concrete piles—These piles are

constructed using steel rods, strands, or wires under tension.The stressing steel is typically enclosed in a wire spiral Non-metallic strands have also been used, but their use is not cov-ered in this report

Prestressed piles can either be pre- or post-tensioned sioned piles are usually cast full length in permanent castingbeds Post-tensioned piles are usually manufactured in sectionsthat are then assembled and prestressed to the required pilelengths in the manufacturing plant or on the job site

Preten-1.1.1.3 Sectional precast concrete piles—These types

of piles are either conventionally reinforced or prestressedpile sections with splices or mechanisms that extend them tothe required length Splices typically provide the full com-pressive strength of the pile, and some splices can providethe full tension, bending, and shear strength Conventionallyreinforced and prestressed pile sections can be combined inthe same pile if desirable for design purposes

1.1.2 Cast-in-place concrete piles—Generally, CIP piles

involve a corrugated, mandrel-driven, steel shell or a driven or mandrel-driven steel pipe; all have a closed end.Concrete is cast into the shell or pipe after driving Thus,unless it becomes necessary to redrive the pile after concreteplacement, the concrete is not subjected to driving stresses.The corrugated shells can be of uniform section, tapered,

top-or stepped cylinders (known as step-taper) Pipe is also able in similar configurations, but normally is of uniformsection or a uniform section with a tapered tip

avail-CIP pile casings can be inspected internally before

con-crete placement Reinforcing steel can also be added

full-length or partial-full-length, as dictated by the design

1.1.3 Enlarged-tip piles—In granular soils, pile-tip

en-largement generally increases pile bearing capacity One

type of enlarged-tip pile is formed by bottom-driving a tube

with a concrete plug to the desired depth The concrete plug

is then forced out into the soil as concrete is added Upon

completion of the base, the tube is withdrawn while

expand-ing concrete out of the tip of the tube; this forms a CIS

con-crete shaft Alternately, a pipe or corrugated shell casing can

be bottom-driven into the base and the tube withdrawn The

resulting annular space (between soil and pile) either closes

onto the shell, or else granular filler material is added to fill

the space The pile is then completed as a CIP concrete pile

In either the CIS or CIP configuration, reinforcing steel can

be added to the shaft as dictated by the design

Another enlarged-tip pile consists of a precast reinforced

concrete base in the shape of a frustum of a cone that is

attached to a pile shaft Most frequently, the shaft is a

corru-gated shell or thin-walled pipe, with the shaft and

enlarged-tip base being mandrel driven to bear in generally granular

subsoils The pile shaft is completed as a CIP pile, and

reinforce-ment is added as dictated by the design Precast, enlarged-tip

bases have also been used with solid shafts, such as timber

piles The precast, enlarged-tip base can be constructed in a

wide range of sizes

1.1.4 Drilled-in caissons—A drilled-in caisson is a special

type of CIP concrete pile that is installed as a high-capacity

unit carried down to and socketed into bedrock These

foun-dation units are formed by driving an open-ended,

heavy-walled pipe to bedrock, cleaning out the pipe, and drilling a

socket into the bedrock A structural steel section (caisson

core) is inserted, extending from the bottom of the rock

socket to either the top or part way up the pipe The entire

socket and the pipe are then filled with concrete The depth

of the socket depends on the design capacity, the pipe

diameter, and the nature of the rock

1.1.5 Mandrel-driven tip—A mandrel-driven tip pile

con-sists of an oversized tip plate driven by a slotted,

steel-pipe mandrel This pile is driven through a hopper

contain-ing enough grout to form a pile the size of the tip plate The

grout enters the inside of the mandrel through the slots as the

pile is driven and is carried down the annulus caused by the

tip plate When the required bearing is reached, the mandrel

is withdrawn, resulting in a CIS shaft Reinforcement can be

lowered into the grout shaft before initial set of the grout

This pile differs from most CIS piles in that the mandrel is

driven, not drilled, and the driving resistance can be used as

an index of the bearing capacity

1.1.6 Composite concrete piles—Composite concrete

piles consist of two different pile sections, at least one of

them being concrete These piles have somewhat limited

applications and are usually used under special conditions

The structural capacity of the pile is governed by the weaker

of the pile sections

A common composite pile is a mandrel-driven corrugatedshell on top of an untreated wood pile Special conditionsthat can make such a pile economically attractive are:

• A long length is required;

• An inexpensive source of timber is available;

• The timber section will be positioned below the nent water table; and

perma-• A relatively low capacity is required

Another common composite pile is a precast pile on top of

a steel H-section tip with a suitably reinforced point A CIPconcrete pile constructed with a steel-pipe lower section and

a mandrel-driven, thin corrugated-steel shell upper section isanother widely used composite pile The entire pile, shell andpipe portion, is filled with concrete, and reinforcing steel can

be added as dictated by the design

1.1.7 Drilled piles—Although driven piles can be

pre-drilled, the final operation involved in their installation isdriving Drilled piles are installed solely by the process ofdrilling

1.1.7.1 Cast-in-drilled-hole pile1—These piles, alsoknown as drilled piers, are installed by mechanically drilling

a hole to the required depth and filling that hole with inforced or plain concrete Sometimes, an enlarged base can

re-be formed mechanically to increase the re-bearing area A steelliner is inserted in the hole where the sides of the hole are un-stable The liner may be left in place or withdrawn as theconcrete is placed In the latter case, precautions are required

to ensure that the concrete shaft placed does not contain arations caused by the frictional effects of withdrawing theliner

sep-1.1.7.2 Foundation drilled piers or caissons—These

are deep foundation units that often function like piles Theyare essentially end-bearing units and designed as deep foot-ings combined with concrete shafts to carry the structureloads to the bearing stratum This type of deep foundation isnot covered in this report, but is included in the reports ofACI 336.1, ACI 336.1R, and ACI 336.3R

1.1.7.3 Auger-grout or concrete-injected piles—These

piles are usually installed by turning a continuous-flight, low-stem auger into the ground to the required depth As theauger is withdrawn, grout or concrete is pumped through thehollow stem, filling the hole from the bottom up This CISpile can be reinforced by a centered, full-length bar placedthrough the hollow stem of the auger, by reinforcing steel tothe extent it can be placed into the grout shaft after comple-tion, or both

hol-1.1.7.4 Drilled and grouted piles—These piles are

in-stalled by rotating a casing having a cutting edge into thesoil, removing the soil cuttings by circulating drilling fluid,inserting reinforcing steel, pumping a sand-cement groutthrough a tremie to fill the hole from the bottom up, andwithdrawing the casing Such CIS piles are used principallyfor underpinning work or where low-headroom conditionsexist These piles are often installed through the existingfoundation

1 Cast-in-drilled-hole piles 30 in (760 mm) and larger are covered in the reference,

“Standard Specification for the Construction of Drilled Piers (ACI 336.1) and

Com-1.1.7.5 Postgrouted piles—Concrete piles can have

grout tubes embedded within them so that, after installation,

grout can be injected under pressure to enhance the contact

with the soil, to consolidate the soil under the tip, or both

CHAPTER 2—DESIGN 2.0—Notation

A = pile cross-sectional area, in.2 (mm2)

A c = area of concrete (including prestressing steel), in.2

(mm2)

= A g – A st, in.2 (mm2) for reinforced concrete piles

A core = area of core of section, to outside diameter of the

spiral steel, in.2 (mm2)

A g = gross area of pile, in.2 (mm2)

A p = area of steel pipe or tube, in.2 (mm2)

A ps = area of prestressing steel, in.2 (mm2)

A sp = area of spiral or tie bar, in.2 (mm2)

A st = total area of longitudinal reinforcement, in.2 (mm2)

d core = diameter of core section, to outside of spiral, in

(mm)

D = steel shell diameter, in (mm)

E = modulus of elasticity for pile material, lb/in.2 (MPa

= N/mm2)

EI = flexural stiffness of the pile, lb-in.2 (N-mm2)

f c′ = specified concrete 28-day compressive strength,

lb/in.2 (MPa)

f pc = effective prestress in concrete after losses, lb/in.2

(MPa)

f ps = stress in prestressed reinforcement at nominal

strength of member, lb/in.2 (MPa)

f pu = specified tensile strength of prestressing steel, lb/in.2

(MPa)

f y = yield stress of nonprestressed reinforcement, lb/in.2

(MPa)

f yh = yield stress of transverse spiral or tie

reinforce-ment, lb/in.2 (MPa)

f yp = yield stress of steel pipe or tube, lb/in.2 (MPa)

f ys = yield stress of steel shell, lb/in.2 (MPa)

g = acceleration of gravity, in./s2 (m/s2)

h c = cross-sectional dimension of pile core, center to

center of hoop reinforcement, in (mm)

I = moment of inertia of the pile section, in.4 (mm4)

I g = moment of inertia of the gross pile section, in.4

(mm4)

k = horizontal subgrade modulus for cohesive soils,

lb/in.2 (N/mm2)

K = coefficient for determining effective pile length

l e = effective pile length = Kl u, in (mm)

l u = unsupported structural pile length, in (mm)

L = pile length, in (mm)

L s = depth below ground surface to point of fixity, in

(mm)

L u = length of pile above ground surface, in (mm)

n h = coefficient of horizontal subgrade modulus, lb/in.3

(N/mm3)

P = axial load on pile, lb (N)

P a = allowable axial compression service capacity, lb (N)

P at = allowable axial tension service capacity, lb (N)

P u = factored axial load on pile, lb (N)

r = radius of gyration of gross area of pile, in (mm)

R = relative stiffness factor for preloaded clay, in

(mm)

s u = undrained shear strength of soil, lb/ft2 (kPa = kN/m2)

s sp = spacing of hoops or pitch of spiral along length of

member, in (mm)

t shell = wall thickness of steel shell, in (mm)

T = relative stiffness factor for normally loaded clay,

granular soils, silt and peat, in (mm)

ρs = ratio of volume of spiral reinforcement to total

vol-ume of core (out-to-out of spiral)

φ = strength reduction factor

φc = strength reduction factor in compression

φt = strength reduction factor in pure flexure, flexure

combined with tension, or pure tension

2.1—General design considerations

Improperly designed pile foundations can perform satisfactorily due to: 1) bearing capacity failure of the pile-soil system; 2) excessive settlement due to compression andconsolidation of the underlying soil; or 3) structural failure

un-of the pile shaft or its connection to the pile cap In addition,pile foundations could perform unsatisfactorily due to: 4) ex-cessive settlement or bearing capacity failure caused by im-proper installation methods; 5) structural failure resultingfrom detrimental pile-installation procedures, or 6) structuralfailure related to environmental conditions

Factors 1 through 3 are clearly design-related; Factors 4and 5 are also design-related, in that the designer can lessenthese effects by providing adequate technical specificationsand outlining proper inspection procedures to be used duringthe installation process Factor 6 refers to environmental fac-tors that can reduce the strength of the pile shaft during in-stallation or during service life The designer can considerenvironmental effects by selecting a pile section to compen-sate for future deterioration, using coatings or other methods

to impede or eliminate the environmental effects, and menting a periodic inspection and repair program to detectand correct structural deterioration Hidden pile defects pro-duced during installation can occur even if the pile design,manufacture, installation, and inspection appear to be flaw-less (Davisson et al 1983) Proper inspection during manu-facture and installation, however, can reduce the incidence

imple-of unforeseen defects The design imple-of the foundation system,preparation of the specifications, and inspection of pile in-stallation should be a cooperative effort between the struc-tural and the geotechnical engineer

In the design of any pile foundation, the nature of the soil and the interaction of the pile-soil system under serviceloads (Factors 1 through 3) are usually the control This re-port does not cover in detail the principles of soil mechanicsand behavior as they can affect pile foundation performance.This chapter does include, however, a general discussion ofthe more important geotechnical considerations related to theproper design of pile foundations For more detailed infor-mation on geotechnical considerations, the reader is referred

sub-to general references on soil mechanics and pile design (for

example, ASCE 1984; NAVFAC DM 7.2 1982; Peck et al.

1974; Prakash and Sharma 1990; Terzaghi et al 1996) and

bibliographies in such references Considerations relating to

Factors 4 and 5 are covered in Chapter 5, although some

guidance on these factors, as well as Factor 6, is offered in

this chapter in connection with the preparation of adequate

technical specifications

With reference to Factor 3, specific recommendations are

given to ensure a pile foundation of adequate structural

capac-ity The design procedures recommended are based on

conser-vative values obtained from theoretical considerations,

research data, and experience with in-service performance

A pile can be structurally designed and constructed to

safely carry the design loads, but the pile cannot be

consid-ered to have achieved its required bearing capacity until it is

properly installed and functioning as a part of an adequate

pile-soil system Thus, in addition to its required design load

structural capacity, the pile must be structurally capable of

being driven to its required bearing capacity This

necessi-tates having one set of structural considerations for driving

and another for normal service Usually, the most severe

stress conditions a pile will endure occur during driving

Three limits to the load-bearing capacity of a pile can be

defined; two are structural in nature, whereas the third

de-pends on the ability of the subsoil to support the pile First,

the pile-driving stresses cannot exceed those that will

dam-age the pile This, in turn, limits the driving force of the pile

against the soil and therefore, the development of the soil’s

capacity to support the pile Second, piles must meet

structur-al engineering requirements under service load conditions,

with consideration given to the lateral support conditions

provided by the soil Third, the soil must support the pile

loads with an adequate factor of safety against a soil-bearing

capacity failure and with tolerable displacements In static

pile load tests carried to failure, it is usually the soil that gives

way and allows the pile to penetrate into the ground; pile

shaft failures, however, can also occur All three of these

lim-its should be satisfied in a proper pile design

2.1.1 Subsurface conditions—Knowledge of subsurface

conditions and their effect on the pile-foundation design and

installation is essential This knowledge can be obtained

from a variety of sources, including prior experience in the

geographical area, performance of existing foundations

un-der similar conditions, knowledge of geological formations,

geological maps, soil profiles exposed in open cuts, and

ex-ploratory borings with or without detailed soil tests From

such information, along with knowledge of the structure to

be supported and the character and magnitude of loading (for

example, column load and spacing), it is often possible to

make a preliminary choice of pile type(s), length(s), and pile

design load(s)

On some projects, existing subsurface data and prior

expe-rience can be sufficient to complete the final foundation

de-sign, with pile driving proceeding on the basis of penetration

resistance, depth of embedment, or both On other projects,

extensive exploration and design-stage pile testing can be

re-quired to develop final design and installation requirements

Subsurface exploration cannot remove all uncertaintyabout subsurface conditions on projects with pile founda-tions Final data on the actual extent of vertical and horizon-tal subsoil variations at a particular site can be obtained fromfield observations during production driving Subsurface in-formation collected by the designer for use in developing thedesign and monitoring pile installation is frequently insuffi-cient to ensure a successful project

A common result of inadequate subsurface exploration ispile-tip elevations that fall below the depth of the deepest ex-ploration This situation often occurs because a pile founda-tion was not considered when exploration started Whereasdeeper exploration will not prevent problems from develop-ing during construction in all cases, information from suchexplorations can be valuable in determining corrective op-tions for solving those problems that do develop The addi-tional cost of deeper exploration during the design stage istrivial compared with the cost of a construction delay re-quired to obtain additional subsoil information on which tobase a decision

Inadequate subsurface exploration of another nature oftendevelops when the decision to use a pile foundation is madeearly in the design process In such cases, there often is a ten-dency to perform detailed exploration of a preconceivedbearing stratum while obtaining only limited data on theoverlying strata that the piles must penetrate This practice isdetrimental because design parameters, such as negative skinfriction, are dependent on the properties of the overlyingstrata Furthermore, a shortage of information on the overly-ing strata can also lead to judgment errors by both the design-

er and the contractor when assessing installation problemsassociated with penetrating the overlying strata and evaluat-ing the type of reaction system most economical for perform-ing static load tests

Test borings should be made at enough locations and to asufficient depth below the anticipated tip elevation of thepiles to provide adequate information on all materials thatwill affect the foundation construction and performance Theresults of the borings and soils tests, taken into considerationwith the function of the piles in service, will assist in deter-mining the type, spacing, and length of piles that should beused and how the piles will be classified (for example, point-bearing piles, friction piles, or a combination of both types)

2.1.1.1 Point-bearing piles—A pile can be considered

point bearing when it passes through soil having low tional resistance and its tip rests on rock or is embedded in amaterial of high resistance to further penetration so that theload is primarily transmitted to the soil at or close to the piletip The capacity of point-bearing piles depends on the bear-ing capacity of the soil or rock underlying the piles and thestructural capacity of the pile shaft Settlement of piles iscontrolled primarily by the compression of materials beneaththe pile tips

fric-2.1.1.2 Friction piles—A friction pile derives its

sup-port from the surrounding soil, primarily through the opment of shearing resistance along the sides of the pile withnegligible shaft loads remaining at the tip The shearing re-sistance can be developed through friction, as implied, or it

devel-may actually consist of adhesion The load capacity of

fric-tion piles depends on the ability of the soil to distribute pile

loads to the soil beneath the pile tip within the tolerable limits

of settlement of the supported structure

2.1.1.3 Combined friction and end-bearing piles—

Combined friction and end-bearing piles distribute the pile

loads to the soil through both shear along the sides of the pile

and bearing on the soil at the pile tip In this classification, both

the side resistance and end-bearing components are of

suffi-cient relative magnitude that one of them cannot be ignored

2.1.2 Bearing capacity of individual piles—A fundamental

design requirement of all pile foundations is that they must

carry the design load with an adequate factor of safety

against a bearing capacity failure Usually, designers

deter-mine the factor of safety against a bearing capacity failure

that is required for a particular project, along with the

foun-dation loads, pile type(s) and size(s) to be used, and an

esti-mate of the pile lengths likely to be required Design should

consider the behavior of the entire pile foundation over the

life of the structure Conditions that should be considered

be-yond the bearing capacity of an individual pile during the

rel-atively short-term installation process are group behavior,

long-term behavior, and settlement

Project specifications prescribe ultimate bearing-capacity

requirements, installation procedures for individual piles, or

both, to control the actual construction of the foundations

Therefore, during construction of the pile foundation, the

de-signer generally exercises control based on the load capacity

of individual piles as installed

An individual pile fails in bearing when the applied load on

the pile exceeds both the ultimate shearing resistance of the

soil along the sides of the pile and the ultimate resistance of

the soil underneath the pile tip The ultimate bearing capacity

of an individual pile can be determined most reliably by static

load testing to failure

Commonly used methods to evaluate the bearing capacity

of the pile-soil system include static pile load testing,

ob-served resistance to penetration for driven piles, and

static-resistance analyses The static-resistance-to-penetration methods

include dynamic driving formulas, analyses based on the

one-dimensional wave equation, and analyses that use

mea-surements of dynamic strain and acceleration near the pile

head during installation All of these methods should be used

in combination with the careful judgment of an engineer

qualified in the design and installation of pile foundations

Frequently, two or more of these methods are used to

evalu-ate bearing capacity of individual piles during design and

construction For example, static load tests to failure (or

proof-load tests to some multiple of the design load) may be

performed on only a few piles, with the remaining production

piles being evaluated on the basis of a

resistance-to-penetra-tion method, calibrated against the static load test results

The design factor of safety against bearing capacity failure

of individual piles for a particular project is dependent on

many variables, such as:

• The type of structure and the implications of failure of

an individual pile on the behavior of the foundation;

• Building code provisions concerning the load

reduc-tions applied (for example, loaded areas) in ing the structural loads applied to the foundations, oroverload allowed for wind and earthquake conditions;

determin-• The reliability of methods used to evaluate bearingcapacity;

• The reliability of methods used to evaluate pile serviceloads;

• The construction control applied during installation;

• The changes in subsoil conditions that can occur withthe passage of time;

• The manner in which soil-imposed loads, such as tive skin friction, are introduced into the factor of safetycalculations;

nega-• The variability of the subsoil conditions at the site; and

• Effects of pile-location tolerances on pile service load

In general, the design factor of safety against a bearing pacity failure should not be less than 2 Consideration of thepreviously stated variables could lead to the use of a higherfactor of safety When the pile capacity is determined solely

ca-by analysis and not proven ca-by static load tests, the designfactor of safety should be higher than normally used withpiles subjected to static load tests

2.1.2.1 Load testing—Static pile load tests may be

per-formed in advance of the final foundation design, in tion with the actual pile foundation installation, or both Testsperformed during the design stage can be used to developsite-specific parameters for final design criteria, make eco-nomical and technical comparisons of various pile types anddesign loads, verify preliminary design assumptions, evaluatespecial installation methods required to reach the desiredbearing strata and capacity, and develop installation criteria.Tests performed as a part of production-pile installation areintended to verify final design assumptions, establish instal-lation criteria, satisfy building code requirements, developquality control of the installation process, and obtain data forevaluating unanticipated or unusual installation behavior.Piles that are statically tested in conjunction with actualpile construction to meet building code requirements, and forquality control, are generally proof-loaded to two times thedesign service load Where practical, and in particular fortests performed before final design, pile load tests should becarried to soil-bearing failure so that the true ultimate bear-ing capacity can be determined for the test conditions.Knowing the ultimate bearing capacity of each type of piletested can lead to a safer or more economical redesign Withknown failure loads, the test results can be used to calibrateother analytical tools used to evaluate individual pile-bearingcapacity in other areas of the project site where static loadtests have not been performed Furthermore, knowledge ofthe failure loads aids evaluation of driving equipment chang-

conjunc-es and any changconjunc-es in installation or dconjunc-esign criteria that can

be required during construction

Sufficient subsoil data (Section 2.1.1) should be available

to disclose dissimilarities between soil conditions at the pile locations and other areas where piles are to be driven.The results of a load test on an individual pile can be applied

test-to other piles within an area of generally similar soil tions, provided that the piles are of the same type and size and

condi-are installed using the same or equivalent equipment,

meth-ods, and criteria as that established by the pile test For a

project site with generally similar soil conditions, enough

tests should be performed to establish the variability in

ca-pacity across the site If a construction site contains dissimilar

soil conditions, pile tests should be conducted within each

area of generally similar subsoil conditions, or in the least

fa-vorable locations, if the engineer can make this distinction

The results of a load test on an individual pile are strictly

applicable only at the time of the test and under the

condi-tions of the test Several aspects of pile-soil behavior can

cause the soil-pile interaction in the completed structure to

differ from that observed during a load test on an individual

pile Some of these considerations are discussed in Sections

2.1.3 through 2.1.6 and Section 2.1.9 On some projects,

spe-cial testing procedures might be warranted to obtain more

comprehensive data for use in addressing the influence of

these considerations on the pile performance under load

These special procedures can include:

• Isolating the pile shaft from the upper nonbearing soils

to ensure a determination of the pile capacity within the

bearing material;

• Instrumenting the pile with strain rods or gages to

determine the distribution of load along the pile shaft;

• Testing piles driven both into and just short of a

point-bearing stratum to evaluate the shear resistance in the

overlying soil as well as the capacity in the bearing

stratum;

• Performing uplift tests in conjunction with downward

compression tests to determine distribution of pile load

capacity between friction and point-bearing;

• Casting jacks or load cells in the pile tip to determine

distribution of pile load capacity between friction and

point-bearing; and

• Cyclic loading to estimate soil resistance distribution

between friction and point-bearing

Where it is either technically or economically impractical

to perform such special tests, analytical techniques and

en-gineering judgment, combined with higher factors of safety

where appropriate, should be used to evaluate the impact of

these various considerations on the individual pile-test

re-sults In spite of the potential dissimilarities between a single

pile test and pile foundation behavior, static load tests on

in-dividual piles are the most reliable method available, both

for determining the bearing capacity of a single pile under

the tested conditions and for monitoring the installation of

pile foundations

Many interpretation methods have been proposed to

esti-mate the failure load from static load test results Numerous

procedures or building code criteria are also used to evaluate

the performance of a pile under static test loading The test

loading procedures and duration required by the various

in-terpretation methods are also highly variable

Acceptance criteria for the various methods are often

based on allowable gross pile-head deflection under the full

test load, net pile-head deflection remaining after the test

load has been removed, or pile-head deflections under the

design load Sometimes, the allowable deflections are

spec-ified as definite values, independent of pile width, length, ormagnitude of load In other methods, the permissible dis-placements can be dependent on only the load, or (in themore rational methods) on pile type, width, length, and load.Some methods define failure as the load at which the slope

of the load-deflection curve reaches a specified value or quire special testing or plotting procedures to determineyield load Other methods use vague definitions of failuresuch as “a sharp break in the load-settlement curve” or “adisproportionate settlement under a load increment.” Thescales used in plotting the test results and the size and dura-tion of the load increments can greatly influence the failureloads interpreted using such criteria These criteria for eval-uating the satisfactory performance of a test pile represent ar-bitrary definitions of the failure load, except where the testpile exhibits a definite plunging into the ground Some defi-nitions of pile failure in model building codes are too liberalwhen applied to high-capacity piles For example, the meth-

re-od that allows a net settlement of 0.01 in./ton (0.029 mm/kN)

of test load might be adequate if applied to low-capacitypiles, but the permitted net settlements are too large when ap-plied to high-capacity piles

This report does not present detailed recommendations forthe various methods for load testing piles, methods, and in-strumentation used to measure pile response under load test,

or the methods of load test interpretation ASTM D 1143,

D 3689, D 3966, and Davisson (1970a, 1972a) discuss theseitems Building codes usually specify how load tests should

be performed and analyzed When the method of analysis isselected by the engineer, however, it is recommended thatthe method proposed by Davisson for driven piles be used.Davisson’s method defines pile failure as the load at whichthe pile-head settlement exceeds the pile elastic compression

by 0.15 in (4 mm) plus 0.83% of the pile width, where thepile elastic compression is computed by means of the expres-sion PL/AE (Davisson 1972a; Peck et al 1974) Davisson’scriterion is too restrictive for drilled piles, unless the resis-tance is primarily friction, and engineers will have to usetheir own judgment or modification

2.1.2.2 Resistance to penetration of piles during

driv-ing—A pile foundation generally has so many piles that it

would be impractical to load- or proof-test them all It is essary to evaluate the bearing capacity of piles that are nottested on the basis of the pile-driving record and the resis-tance to penetration during installation Final driving resis-tance is usually weighted most heavily in this evaluation.Driving criteria based on resistance to penetration are ofvalue and often indispensable in ensuring that all piles aredriven to relatively uniform capacity This will minimizepossible causes of differential settlement of the completedstructure due to normal variations in the subsurface condi-tions within the area of the pile-supported structures In ef-fect, adherence to an established driving resistance tends topermit each pile to seek its own length to develop the re-quired capacity, thus compensating for the natural variations

nec-in depth, density, and quality of the bearnec-ing strata

For over a century, engineers have tried to quantify the lationship between the ultimate bearing capacity of a pile and

re-the resistance to penetration observed during driving The

earlier attempts were based on energy methods and

Newto-nian theory of impact (Section 2.1.2.3) The shortcomings of

dynamic pile-driving formulas have long been known

(Cum-mings 1940), yet they still appear in building codes and

spec-ifications The agreement between static ultimate bearing

capacity and the predicted capacity based on energy formulas

are in general so poor and erratic that their use is not justified,

except under limited circumstances where the use of a

partic-ular formula is justified by prior load tests and experience in

similar soil conditions with similar piles and driving

assem-blies (Olson and Flaate 1967; Terzaghi et al 1996)

Cummings (1940) suggested that the dynamics of pile

driving be investigated by wave-equation analysis With the

advent of the computer, the one-dimensional wave-equation

analysis of pile driving has become an indispensable tool for

the foundation engineer (Section 2.1.2.4) Field

instrumenta-tion that measures and records shaft strain and accelerainstrumenta-tion

near the pile top has become available and has spawned

at-tempts to predict the ultimate bearing capacity using these

measurements (Section 2.1.2.5)

Although the development of the wave-equation analysis

and methods based on strain and acceleration measurements

represents a vast improvement over the fundamentally

un-sound dynamic formulas, these refined methods are not a

re-liable substitute for pile load tests (Selby et al 1989;

Terzaghi et al 1996) Some driving and soil conditions

de-feat all of the geotechnical engineer’s tools except the static

load test (Davisson 1989; Prakash and Sharma 1990) Such

problems have occurred with the wave equation as well as

with methods based on dynamic measurements (Davisson

1991; Terzaghi et al 1996)

In spite of their short comings, resistance-to-penetration

methods of estimating bearing capacity, based on the wave

equation, remain a valuable tool because of the

impracticali-ty of testing all piles on a project, their use as a design tool

for evaluating the pile driveability and driving stresses, and

their use in equipment selection Static load tests are still

needed to confirm bearing capacity and calibrate the

penetra-tion-resistance method used to extend quality control over

the remaining piles In some instances, the increased use of

dynamic measurements has actually been associated with an

increase in the frequency of performing static load tests

be-cause such load test data are required to calibrate the capacity

predictions (Schmertmann and Crapps 1994)

2.1.2.3 Dynamic formulas—Piles are long members,

with respect to their width, and do not behave as rigid bodies

Under the impact from a hammer, time-dependent stress

waves are set up in the pile and surrounding soil All of the

dynamic formulas ignore the time-dependent aspects of

stress-wave transmission and are, therefore, fundamentally

unsound

The term “dynamic formula” is misleading as it implies a

determination of the dynamic capacity of the pile Such

for-mulas have actually been developed to reflect the static

capac-ity of the pile-soil system as measured by the dynamic

resistance during driving This is also true of the

wave-equa-tion analysis and methods based on strain and accelerawave-equa-tion

measurements (Sections 2.1.2.4 and 2.1.2.5) Under certainsubsoil conditions, penetration resistance as a measure of pilecapacity can be misleading in that it does not reflect such soilphenomena as relaxation or freeze (Section 2.4.5), which caneither reduce or increase the final static pile-soil capacity.Dynamic formulas, in their simplest form, are based onequating the energy of a hammer blow to the work done asthe pile moves a distance (set) against the soil resistance Themore complicated formulas also involve Newtonian impactprinciples and other attempts to account for the many indi-vidual energy losses within the hammer-capblock-pile-soilsystem These formulas are used to determine the requiredresistance to penetration [blows per in (mm)] for a givenload or to determine the load capacity based upon a givenpenetration resistance or set

Some dynamic formulas are expressed in terms of ultimatepile capacity, whereas others are expressed in terms of allow-able service capacity All dynamic formulas are empiricaland provide different safety factors, often of unknown mag-nitude In general, such formulas are more applicable to non-cohesive soils The applicability of a formula to a specificpile-soil system and driving conditions can be evaluated byload tests to failure on a series of piles

Dynamic formulas have been successfully used when plied with experience and judgment and with proper recog-nition of their limitations Because the formulas arefundamentally unsound, however, there is no reason to ex-pect that the use of a more complicated formula will lead tomore reliable predictions, except where local empirical cor-relations are known for a given formula under a given set ofsubsurface conditions

ap-When pile capacity is to be determined by a dynamic mula, the required penetration resistance should be verified

for-by pile load tests, except where the formula has been

validat-ed by prior satisfactory experience for the type of pile andsoil involved Furthermore, such practices should be limited

to relatively low pile capacities Attempts to use empiricalcorrelations for a dynamic formula determined for a givenpile type and site condition with other pile types and differentsite conditions can lead to either ultraconservative or unsaferesults

2.1.2.4 Wave-equation analysis—The effects of

driv-ing a pile by impact can be described mathematically ing to the laws of wave mechanics (Isaacs 1931; Glanville et

accord-al 1938) Cummings (1940) discussed the defects of the namic formulas that do not consider the time-dependent as-pects of stress-wave transmission and pointed out the merits

dy-of using wave mechanics in making a rational analysis dy-of thepile-driving process

Early developments in application of the wave-equationanalysis to pile driving were advanced by Smith (1951, 1955,1962) The advent of high-speed digital computers permittedpractical application of wave-equation analysis to pile equip-ment design and the prediction of pile driving stress and stat-

ic pile capacity The first publicly available digital computerprogram was developed at Texas A&M University (Edwards1967)

Over the past 30 years, wave-equation analysis has taken

its place as a standard tool used in pile foundation design and

construction control Through the sponsorship of the Federal

Highway Administration, wave-equation programs are

readily available through public sources (Goble and

Rausche 1976, 1986; Hirsch et al 1976), as well as from

several private sources Today, with both wave-equation

analysis software and computer hardware readily available

to engineers, there is no reason to use dynamic formulas

The one-dimensional wave equation mathematically

de-scribes the longitudinal-wave transmission along the pile

shaft from a concentric blow of the hammer (Edwards 1967;

Hirsch et al 1970; Lowery et al 1968, 1969; Mosley and

Raamot 1970; Raamot 1967; Samson et al 1963; Smith

1951, 1955, 1962) Computer programs can take into

ac-count the many variables involved, especially the elastic

characteristics of the pile The early programs were deficient

in their attempts to model diesel hammers, but research in

this area has improved the ability of modern programs to

perform analysis for this type of hammer (Davisson and

Mc-Donald 1969; Goble and Rausche 1976, 1986; Rempe 1975;

Rempe and Davisson 1977)

In wave-equation analysis of pile driving, an ultimate pile

capacity (lb or N) is assumed for a given set of conditions,

and the program performs calculations to determine the net

set (in or mm) of the pile The reciprocal of the set is the

driving resistance, usually expressed in hammer blows per

in (mm) of pile penetration The analysis also predicts the

pile shaft forces as a function of time after impact, which can

be transformed to the driving stresses in the pile cross

sec-tion The process is repeated for several ultimate resistance

values From the computer output, a curve showing the

rela-tionship between the ultimate pile capacity and the

penetra-tion resistance can be plotted The maximum calculated

tensile and compressive stresses can also be plotted as a

function of either the penetration resistance or the ultimate

load capacity In the case of diesel hammers and other

vari-able-stroke hammers, the analysis is performed at several

different strokes (or equivalent strokes in the case of

closed-top diesel hammers) to cover the potential stroke range that

might develop in the field

Although results are applicable primarily to the set of

con-ditions described by the input data, interpolations and

ex-trapolations for other sets of conditions can be made with

experience and judgment Routine input data describing the

conditions analyzed include such parameters as hammer ram

weight; hammer stroke; stiffness and coefficient of

restitu-tion of the hammer cushion (and pile cushion if used); drive

head weight; pile type, material, dimensions, weight, and

length; soil quake and damping factors; percentage of pile

capacity developed by friction and point bearing; and the

distribution of frictional resistance over the pile length With

diesel hammers, the model must deal with the effects of gas

force on the hammer output and the steel-on-steel impact

that occurs as the ram contacts the anvil

Wave-equation analysis is a reliable and rational tool for

evaluating the dynamics of pile driving and properly takes

into account most of the factors not included in the other

dy-namic formulas (Section 2.1.1.3) Although wave-equationanalysis is based on the fundamentally sound theory of one-dimensional wave propagation, it is still empirical The pri-mary empirical content are the input parameters andmathematical model for the soil resistance Fortunately, thesimple mathematical soil model and empirical coefficientsproposed by Smith (1951, 1955, 1962) appear to be adequatefor approximating real soil behavior in a wide variety of, butnot all, driving conditions

Except for conditions where unusually high soil quake ordamping are encountered, a wave-equation analysis coupledwith a factor of safety of 2 can generally provide a reasonabledriving criterion, providing proper consideration is given tothe possible effect of soil freeze or relaxation (Section 2.4.5).When the required pile penetration resistance is determined

by a wave-equation analysis, the results of such analysis andthe pile capacity should be verified by static load test Withpile load tests carried to failure, adjustments in the soil-inputparameters can be made if necessary to calibrate the waveequation for use at a given site Information from dynamicmeasurements and analysis (Section 2.1.2.5) can also assist

in refining input to the wave-equation analysis concerninghammer, cushion, pile, and soil behavior

The wave equation is an extremely valuable design toolbecause the designer can perform analyses during the designstage of a pile foundation to evaluate both pile driveabilityand pile-driving stresses for the various stages of installation.These results aid in making design decisions on pile-drivingequipment for the pile section ultimately selected and ensur-ing that the selected pile can be installed to the required ca-pacity at acceptable driving stress levels For precast piles,the analysis is most helpful for selecting the hammer and pilecushioning so that the required pile load capacity can be ob-tained without damaging the pile with excessive drivingstresses (Davisson 1972a) Such analyses are also useful inestimating the amount of tension, if any, throughout the pilelength as well as at proposed splice locations This is espe-cially important in the case of precast and prestressed pilesthat are much weaker in tension than in compression Adriveability study can be used to aid in developing designand specification provisions related to equipment selectionand operating requirements, cushioning requirements,reinforcing or prestressing requirements, splice details, andpreliminary driving criteria Therefore, it is possible to de-sign precast and prestressed piles with greater assurance thatdriving tensile and compressive stresses will not damage thepile The wave-equation analysis, however, does not predicttotal pile penetration (pile embedment)

2.1.2.5 Dynamic measurements and

analysis—Instru-mentation and equipment are available for making ments of dynamic strains and accelerations near the pile head

measure-as a pile is being driven or restruck Procedures for makingthe measurements and recording the observations are cov-ered in ASTM D 4945

The measured data, when combined with other tion, can be used in approximate analytical models to evalu-ate dynamic pile-driving stresses, structural integrity, staticbearing capacity, and numerous other values blow by blow

informa-while the pile is being driven (Rausche et al 1972, 1985).

Subsequently, the recorded information can be used in more

exact analysis (Rausche 1970; Rausche et al 1972, 1985)

that yield estimates of both pile bearing capacity and

soil-re-sistance distribution along the pile Determination of static

pile capacity from the measurements requires empirical input

and is dependent on the engineering judgment of the

individ-ual performing the evaluation (ASTM D 4945; Fellenius

1988) The input into the analytical models may or may not

result in a dynamic evaluation that matches static load test

data It is desirable and may be necessary to calibrate the

re-sults of the dynamic analysis with those of a static pile load

test (ASTM D 4945)

Dynamic measurements and analyses can provide design

information when site-specific dynamic measurements are

obtained in a pile-driving and load-testing program

undertak-en during the design phase of a project Without such a test

program, the designer must decide on the type of pile, size of

pile, and the pile-driving equipment relying on other

tech-niques and experience The wave-equation analysis is a very

useful design tool that helps provide information leading to

the necessary design decisions (Section 2.1.2.4) Dynamic

measurements and analyses find use in the verification of the

original design and development of final installation criteria

after production pile driving commences The ability to make

dynamic measurements is a useful addition to the

geotechni-cal engineer’s resources when properly used There are,

how-ever, limitations to the use of this method in determining

static pile load capacity and these methods are not a reliable

substitute for pile load tests (Selby et al 1989; Terzaghi et al

1996)

2.1.2.6 Static-resistance analysis—The application of

static analysis uses various soil properties determined from

laboratory and field tests, or as assumed from soil boring

da-ta The pile capacity is estimated by applying the shearing

re-sistance (friction or adhesion) along the embedded portion of

the pile and adding the bearing capacity of the soil at the pile

point Such analyses, insofar as possible, should reflect the

effects of pile taper, cross-sectional shape (square, round)

and surface texture, the compaction of loose granular soils by

driving displacement-type piles, and the effects of the

instal-lation methods used Each of these factors can have an

influ-ence on the final load-carrying capacity of a pile (Nordlund

1963) When pile length is selected on the basis of

experi-ence or static-resistance analysis, static load tests should be

performed to verify such predictions

2.1.2.7 Settlement—The investigation of the overall

pile foundation design for objectionable settlement involves

the soil properties and the ability of the soil to carry the load

transferred to it without excessive consolidation or

displace-ment, which in time could cause settlements beyond that for

which the structure is designed The soils well below the pile

tips can be affected by loading, and such effects vary with the

magnitude of load applied and the duration of loading Many

of the design considerations discussed in this chapter relate

to the evaluation of settlement The soil mechanics involved

are beyond the scope of this report The long-term settlement

of a pile foundation under service loading is not the same as

the settlement observed in a short-term static load test on anindividual pile (Section 2.1.9)

2.1.3 Group action in compression—The bearing capacity

of a pile group consisting of end-bearing piles or piles driveninto granular strata at normal spacing (Section 2.1.4) can beconsidered to be equal to the sum of the bearing capacities ofthe individual piles The bearing capacity of a friction pilegroup in cohesive soil should be checked by evaluating theshear strength and bearing capacity of the soil, assuming thatthe pile group is supported by shear resistance on the periph-ery of the group and by end bearing on the base area of thegroup The use of group reduction formulas based on spacingand number of piles is not recommended

2.1.4 Pile spacing—Pile spacing is measured from center

to center The minimum recommended spacing is three timesthe pile diameter or width at the cutoff elevation Several fac-tors should be considered in establishing pile spacing Forexample, the following considerations might necessitate anincrease in the normal pile spacing:

A For piles deriving their principal support from friction;

B For extremely long piles, especially if they are ble, minimize tip interference;

flexi-C For CIS concrete piles where pile installation coulddamage adjacent unset concrete shafts;

D For piles carrying very high loads;

E For piles that are driven in obstructed ground;

F Where group capacity governs;

G Where passive soil pressures are considered a majorfactor in developing pile lateral load capacity;

H Where excessive ground heave occurs;

I Where there is a mixture of vertical and batter piles;and

J Where densification of granular soils can occur.Special installation methods can be used as an alternative-

to increasing pile spacing For example, predrilling for Cases

B, E, and H above, or staggered installation sequence forCase C Closer spacing might be permitted for end-bearingpiles installed in predrilled holes Under special conditions,the pile spacing might be determined by the available con-struction area

2.1.5 Stability—All piles or pile groups should be stable.

For normal-sized piling, stability will be provided by pilegroups consisting of at least three piles supporting an isolat-

ed column Wall or strip footings not laterally supportedshould be carried by a staggered row of piles Two-pilegroups are stable if adequately braced in a direction perpen-dicular to the line through the pile centers Individual pilesare stable if the pile tops are laterally braced in two directions

by construction, such as a structural floor slab, grade beams,struts, or walls

2.1.6 Lateral support—All soils, except extremely soft

soils (s u less than 100 lb/ft2 [5 kPa]), will usually providesufficient lateral support to prevent the embedded length ofmost common concrete-pile cross sections from buckling un-der axial load In extremely soft soil, however, very slenderpile sections can buckle All laterally unsupported portions

of piles should be designed to resist buckling under all

load-ing conditions and should be treated as columns in

determin-ing effective lengths and buckldetermin-ing loads

2.1.7 Batter piles—Batter piles are commonly used to

re-sist large horizontal forces or to increase the lateral rigidity

of the foundation under such loading When used, batter

piles tend to resist most, if not all, of the horizontal loading

The design should reflect this type of behavior The use of

batter piles to resist seismic forces requires extreme care

be-cause these piles restrain lateral displacement and may

re-quire unattainable axial deformation ductility When batter

piles are used, a complete structural analysis that includes

the piles, pile caps, structure, and the soil is necessary if the

forces are to be properly accounted for, including the

possi-bility of tension developing in some piles Saul (1968),

Hrennikoff (1950), and Reese and et al (1970) have reported

suitable analyses

When batter piles are used together with vertical piles, the

design of the foundation structure should consider that the

batter piles will accept a portion of the vertical load The

in-clination and position of the batter piling should be selected

so that when a lateral load is applied, the resultant of the

lat-eral and vertical loadings is axial, and the effects of bending

moments are kept to a minimum Bending stresses due to the

weight of the pile itself, such as those that occur for a long

freestanding portion of a batter pile in marine structures,

should be taken into consideration

2.1.8 Axial-load distribution—Axial-load distribution

in-cludes both rate of transfer of load from the pile to the soil

and distribution of load between friction and point bearing

(soil-resistance distribution) The distribution of load can be

approximated by theoretical analysis, special load-test

meth-ods, or properly instrumenting load-test piles Any

theoreti-cal analysis of distribution of load between pile and soil

should take into account all the factors, such as type of soil

and soil properties, vertical arrangement and thickness of

soil strata, group behavior, type of pile (including pile

material, surface texture, and shape), and effects of time

The full design load can be considered to act on the pile

down to the surface of the soil layer that provides permanent

support Below that level, the loads applied to the pile will

be distributed into the soil at rates that will vary with the type

of soil, type and shape of pile, and other factors

Even for piles classified as point-bearing, some part of the

load may be transferred from the pile to the soil along that

portion of the pile embedded in soil that provides permanent

lateral support Where negative skin friction conditions exist

(Sections 2.1.9.1 and 2.2.2.2), the full pile load, including

the negative friction load, should be considered to act at the

top of the bearing stratum Davisson (1993) provides

analy-ses and case histories of negative skin friction effects

2.1.9 Long-term performance—Every pile foundation

represents an interaction between the piles and the

subsur-face materials that surround and underlie the foundation In

the design of pile foundations, it is imperative to consider the

changes in subsoil conditions that can occur with the passage

of time and adversely affect the performance of the

founda-tion Typical consequences of possible changes are

long-term consolidation of the soil that surrounds or underlies the

piles, lateral displacements due to unbalanced vertical loads

or excavations adjacent to the foundations, consolidation fects of vibrations and fluctuation in ground water, andscour It is sometimes neither possible nor practical to eval-uate the effects of such changes by means of pile load tests

ef-In many instances, judgment decisions should be made based

on a combination of theory and experience Some of thesepossible changes in subsurface conditions, however, are notpredictable and thus cannot be evaluated accurately by thedesigning engineer

2.1.9.1 Long-term consolidation and negative skin

friction—If piles extend through soft compressible clays and

silts to final penetration into suitable bearing material, theupper strata can carry some portion of a test load or workingload by friction The frictional capacity of these compress-ible upper strata could be temporary, however, and pro-longed loading can cause consolidation of these soils, with

an increasing part of the design dead load being carried bythe underlying bearing material Under such conditions, tem-porary live loads may not have a major effect on the load dis-tribution Analyses of long-term effects should be performed

by qualified professionals who have adequate informationabout the project

Moreover, if new fill or other superimposed loads areplaced around the pile foundation, consolidation of the sub-surface soft soils can occur and the positive skin friction overthe upper portion of the piles can be reversed completely,causing negative skin friction (or downdrag) and an increase

in the total load that will be carried by the piles (Section

2.2.2.2) If subsoil conditions are of this type, data from loadtests conducted on piles of different length, piles instrument-

ed to reveal actual load distribution, or piles cased off throughthe consolidation zone, together with the results of laboratorytests that evaluate the stress-strain properties of the subsoil,can be used to determine appropriate design criteria

Possible long-term settlements due to the consolidation ofcompressible strata located beneath, or even at considerabledepth below the pile tip, should be evaluated Such settle-ments of pile groups and entire foundations cannot be evalu-ated by means of load tests alone They can, however, beestimated with a reasonable degree of accuracy by means ofappropriate soil borings, soil samples, laboratory tests, andsoil mechanics theory

2.1.9.2 Lateral displacement—Pile foundations for

re-taining walls and abutments, as well as many other types ofstructures, can be acted upon by lateral forces developed inthe subsoil beneath the structures Such deep-seated lateralforces against pile foundations are commonly due to unbal-anced vertical loads produced by such things as the addedweight of adjacent fill or reduction in subsoil pressurescaused by adjacent excavation If the subsoil consists of ma-terial susceptible to long-term lateral movements, displace-ments of pile foundations can be progressive and becomevery large Moreover, under such conditions, piles can besubjected to large shear and flexural stresses and be designedaccordingly

2.1.9.3 Vibration consolidation—If a friction pile

foundation in loose granular soil is subjected to excessive

vi-brations, unacceptable settlements can occur as a result of the

densification of the granular soil that surrounds or underlies

the piles The design of pile foundations under such

condi-tions calls for judgment and experience in addition to

theoretical analysis based on adequate subsoil data It may be

necessary to develop the pile capacity within strata below

those affected by the vibrations

2.1.9.4 Groundwater—The design should consider

the possible effects of groundwater fluctuations on the

long-term performance of pile foundations Lowering at the

groundwater level can cause consolidation of soft clay and

plastic silt If such compressible strata surround or underlie

the piles, then consolidation can result in negative skin

fric-tion loads and settlement of the foundafric-tions On the other

hand, a rise in the groundwater table in loessial soil can cause

settlement of friction-pile foundations if they are subjected to

vibrations or shock loadings Also, certain types of clay soils

are subject to shrinking or swelling as the moisture content

changes; this could adversely affect the pile-foundation

per-formance Under such conditions, take steps to isolate the

pile from the zone of variable moisture content and develop

the pile capacity in the soils of constant moisture content or,

as an alternative, take whatever precautions are necessary to

maintain a fairly constant moisture content in the soils If

swelling of the soil could occur before the full load is on the

pile (or for lightly loaded piles), it may be necessary to

pro-vide tension reinforcement in the pile

For pile foundations bearing in sand, raising the water

ta-ble results in an effective stress decrease and a corresponding

reduction in pile bearing capacity This phenomenon

com-monly occurs where piles are driven in a deep excavation

where temporary dewatering has taken place

2.1.9.5 Scour—For pile foundations of bridges or

oth-er structures ovoth-er watoth-er, or for structures adjacent to watoth-er

subject to wave action that might undermine the foundation,

the possibility of scour should be considered in the design

Where upper soil materials can be removed by scour, the

piles must have adequate capacity produced by sufficient

penetration below the depth of scour for the various loading

conditions Furthermore, that portion of the pile extending

through the zone of possible scour should be designed to

resist buckling (Section 2.3.4)

2.1.10 Lateral capacity—Lateral forces on piles will depend

on the environment and function of the supported structure,

and can be produced by wind, waves, ships, ice action, earth

pressures, seismic action, or mechanical causes Batter piles

are frequently used to resist lateral loads (Section 2.1.7)

The ability of vertical piles to resist lateral loads depends

upon such things as pile type, material, and stiffness; subsoil

conditions; embedment of pile, pile cap, and foundation wall

in the soil; degree of fixity of pile to cap connection; pile

spacing; and the existence and magnitude of axial loads

Group-effect limitations are more severe for laterally loaded

piles than for those with axial loads only (Davisson 1970b)

In evaluating the lateral capacity of vertical piles, the soil

resistance against the pile, pile cap, and foundation walls

should be considered Soil resistance can contribute

substan-tially to the lateral capacity of a pile group or pile foundation,

providing that the soil is present for the loading conditionsunder consideration The presence of axial compressiveloads can contribute to the pile’s lateral (bending) capacity

by reducing tension stresses caused by bending due to lateralloads Design methods for lateral loading of concrete pilesshould consider axial loads, whether compression or tension,and lateral soil resistance If lateral load capacity is critical,

it should be investigated or verified by field tests under

actu-al in-service loading conditions, including the verticactu-al deadload that could be considered permanent

2.1.11 Uplift capacity—Engineers should exercise caution

when applying tension pile load test results to the design ofthe tension-resisting portion of a structure Because of thenature of tension test configurations, a tension load test mea-sures only the ability of a pile to adhere to the soil In service,however, the tension capacity is limited to how much soilweight (buoyant weight) the pile can pickup without exceed-ing the adhesion to the pile Therefore, the geometric charac-teristics (pile length, shape, and spacing) of the pile-soilsystem also come into play

For an interior pile in a group of piles, the ultimate tension capacity is limited to the buoyant weight of the soilvolume defined by the square of the pile spacing times thepile length Exterior piles in a group of piles can attach tomore soil, but no general agreement exists at this time on theamount

pile-In summary, the tension capacity for a foundation is

limit-ed by both the adhesion to the pile developlimit-ed from a load testand the amount of soil buoyant weight available to resist ten-sion The lower capacity indicated for these two limits isused

2.2—Loads and stresses to be resisted

Stresses in piles result from either temporary or permanentloads Temporary stresses include those the pile may be sub-jected to before being put into service (such as handling anddriving stresses) and stresses resulting from in-service load-ing of short and intermittent duration (such as wind, wave,ship and other impact loads, and seismic loading) Perma-nent stresses include those resulting from dead and live loads

of relatively prolonged duration

The piles and the soil-pile system must be able to resist theservice (unfactored) loads in all reasonable combinations.These forces should not cause excessive foundation defor-mations, settlement, or other damage Furthermore, thereshould not be a collapse of the foundation system at the fac-tored loads The pile should be designed to resist the maxi-mum forces that could reasonably occur, regardless of theirsource The factored ultimate load combinations in ACI 318-95

or other controlling codes should be considered

2.2.1 Temporary loads and stresses 2.2.1.1 Handling stresses—Concrete piles that are lift-

ed, stored, and transported are subjected to substantial dling stresses Bending and buckling stresses should beinvestigated for all conditions, including handling, storing,and transporting For lifting and transporting stresses, the anal-ysis should be based on 150% of the weight of the pile to allowfor impact Pickup and blocking points should be arranged and

han-clearly marked so that all stresses are within the allowable

limits and cracking does not occur (Chapters 4 and 5)

2.2.1.2 Driving stresses—Driving stresses are

com-plex functions of pile and soil properties and are influenced

by the required driving resistance, the type and operation of

the equipment used, and the method of installation Both

compressive and tensile stresses occur during driving and

can exceed the yield or tensile cracking strengths of the pile

material Dynamic compressive stresses during driving are

usually considerably higher than the static compressive

stresses resulting from the service load

The design of the pile and the driving system should

pro-vide adequate structural strength to resist the expected

driv-ing stresses without damagdriv-ing the pile Generally, these

installation stresses can be evaluated during design by

wave-equation analysis (Section 2.1.2.4) During construction,

dy-namic measurements can also provide useful information for

evaluating driving stresses (Section 2.1.2.5)

2.2.1.3 Tensile and shear stresses—Piles are

some-times subjected to temporary axial tensile stresses resulting

from such things as wind, hydrostatic forces, seismic action,

and the swelling of certain type of clays when the moisture

content increases Bending and shear stresses of a temporary

nature can result from seismic forces, wind forces, and wave

action or ship impact on waterfront and marine structures

2.2.1.4 Seismic stresses—Earthquake loads on pile

foundations can be both lateral and vertical, and result

prima-rily from horizontal and vertical ground accelerations

trans-mitted to the structure by ground action on the piles The

magnitude of the ground motion transmitted to the structure,

and thus the loads applied to the foundation, depend on the

subsoil conditions, the method of transfer of load from pile

to soil (whether friction or point bearing), and the type of

construction and the connection between the structure and

the foundation The magnitude of the loads transmitted back

to the piles by the structure depends on the extent of the

vi-brations of the structure and the weight and flexibility of the

structure

The lateral load or base shear at the pile head results from

the inertia of the structure at the start of earthquake

vibra-tions and the momentum of the structure as it is moved

lat-erally The actual value of the base shear is a function of the

magnitude of the earthquake, the degree of seismicity of the

geographical area, and the fundamental period of the

struc-ture at a reasonable, actual in-service mass of the strucstruc-ture

To help distribute the base shear in a building, individual

pile caps are often interconnected with reinforced concrete

struts capable of withstanding the horizontal force resulting

from an earthquake, both in compression and tension

During an earthquake, uplift and compression loads can

be exerted on the pile foundation as the structure tends to

overturn Batter piles supporting bulkheads of wharves have

suffered great distress because they tend to resist all of the

horizontal force in the structure, leading to failure of either

the pile or the pile cap supported by the pile Longer, more

flexible batter piles have performed better Other pile

fail-ures have occurred because of poor connection details

be-tween the piles and the cap, lack of adequate strength androtational ductility in the pile section, and because of faultyanalyses

Design and detailing of piles to resist seismic forces andmotions are discussed in Section 2.3.6

2.2.2 Permanent loads and stresses 2.2.2.1 Dead- and live-load stresses—Dead and live loads

cause compressive, tensile, bending, and shear stresses, orcombinations of these stresses, in piles The calculation ofthe compressive force to be carried by a pile should be based

on the total dead load and the live load that is reasonably pected to be imposed on the pile Service live loads are re-duced in accordance with accepted engineering principlesand the governing building code The magnitude of the re-sulting compressive force can vary along the pile length ac-cording to the distribution of the load into the soil (Section

ex-2.1.8)

Some tension forces can be fairly permanent, such as thosedue to prolonged hydrostatic pressure Tension in the pilecan dissipate with depth below the ground surface, depend-ing on subsoil conditions, pile type, and other factors.Tall, slender structures, such as chimneys, power-trans-mission structures, and towers, are very sensitive to lateralloads The forces that can be induced in piles of such struc-tures should be carefully investigated for all possible loadingcombinations and load-factor combinations to ensure that themost critical pile forces in both tension and compression areidentified

Horizontal and eccentric loads cause bending stresses inthe piles and affect the distribution of the total axial load toindividual piles in the group For evaluating bending andshear stresses in piles due to horizontal loads or moments (orboth) applied at or above the ground surface, the distribution

of moment and shear forces along the pile axis should be termined by flexural analysis including the horizontal sub-grade reaction of the soil Nondimensional solutions based

de-on the theory of a beam de-on elastic foundatide-ons (Hetenyi1946) are available for a variety of distributions of horizontalsubgrade modulus with depth (Reese and Matlock 1956;Matlock and Reese 1962; Broms 1964a, 1964b, 1965; Davis-son 1970b; NAVFAC DM-7.2 1982; Prakash and Sharma1990) The value of the horizontal subgrade modulus used inthe analysis should consider group effects and, wherewarranted, the influence of cyclic loading (Davisson 1970b)

In such analyses, the flexural stiffness of the pile shaft EI can be taken as the calculated EI g for the gross section, un-less the horizontal loads and moments, when acting with theapplicable concurrent axial loads, are sufficient to causecracking over a significant length of the pile When the mag-nitude of the applied horizontal loads and moments are suf-ficient to cause cracking along a significant portion of thepile, the flexural stiffness can be calculated in accordancewith the recommendations of Section 9.5 of ACI 318-95 (ef-fective moment of inertia) or Sections 10.11 to 10.13 (ap-proximate evaluation of slenderness effects), unless a morerefined analysis is used

Where more detailed analyses are required to account forcomplex variations of the subgrade modulus with depth,

variations in flexural stiffness EI of the pile shaft along the

length, or the nonlinear behavior of the horizontal soil

reac-tions with deflection, computer programs can be used to

solve the beam on elastic foundation problems in finite

dif-ference form (Matlock and Reese 1962; Reese 1977)

Consideration of nonlinear soil behavior leads to nonlinear

relationships between the applied loads and the resulting

mo-ment and shear distribution along the pile Therefore, when

the designer has sufficient information on soil properties to

define accurately the horizontal soil reaction relationships

(p-y curves), and the conditions warrant the use of nonlinear

soil reactions, the distribution of the factored moment and

factored shear along the pile axis should be determined by

performing the analysis using the applied factored horizontal

loads and moments The influence of a nonlinear soil

resis-tance-deflection relationship can also be determined using

nondimensional solutions in an iterative procedure (Prakash

and Sharma 1990)

In some structures, second-order deflection (P-∆) effects

can become important In such cases, the foundations must

be designed to resist the increased forces associated with

these effects

2.2.2.2 Negative skin friction—Downward movement

of the soil with respect to the pile, resulting from

consolida-tion of soft upper layers through which the pile extends or the

shrinkage of certain types of clay soils when the moisture

content decreases, produces negative skin friction loading on

the pile Consolidation is generally caused by an additional

load being applied at the ground surface, such as from a

re-cently placed fill, or by lowering of the water table, and

con-tinues until a state of equilibrium is reached again Under

negative friction conditions, the critical section of the pile

can be located at the surface of the permanent bearing strata

The magnitude of this load is limited by certain factors, such

as the shearing resistance between the pile surface and the

soil, the internal shear strength of the soil, the pile shape, and

the volume of soil affecting each pile (Davisson 1993)

Neg-ative skin friction loads should be considered when

evaluat-ing both the soil bearevaluat-ing capacity and the pile shaft strength

requirements If it is necessary to use batter piles under

con-ditions where negative skin friction can develop, the designer

must consider both the additional axial negative skin friction

loads and the additional bending loads from the weight of the

settling soil and drag forces on the pile sides

2.3—Structural strength design and allowable

service capacities

2.3.1 General approach to structural capacity—The most

common use of foundation piles is to provide foundation

sup-port for structures, with axial compression frequently being

the primary mode of pile loading Building codes and

regula-tory agencies limit the allowable axial service capacities for

various pile types based on both soil-pile behavior and on

structural-material behavior Although the permissible pile

capacity is frequently controlled by the soil-pile behavior in

terms of soil bearing capacity or tolerable displacements, it is

also possible for the structural strength of the pile shaft to

control this capacity in some cases

Historically, the structural design of foundation piles hasbeen on an allowable service capacity basis, with most build-ing codes and regulatory agencies specifying the structuralrequirements for the various types of piling on an allowable

unit stress basis For example, both the Uniform Building

Code (1994) and the BOCA National Building Code (1993)

limit the allowable concrete compressive stress for CIP

con-crete piles to 0.33 f′c and provide provisions for the allowablestress to be increased by concrete confinement (up to a max-

imum value of 0.40 f′c ) provided required conditions are met.Similarly, both of these codes limit the allowable compres-

sive stress on prestressed concrete piles to (0.33 f c ′– 0.27f pc).These allowable unit stresses were first published around

1970 and are for the conditions of a fully embedded and erally supported pile They were based on strength designconcepts (Davisson et al 1983; Fuller 1979; PCA 1971) andwere also the basis of previous recommendations of thiscommittee

lat-Whereas axial compression may often be the primarymode of loading, concrete piles are also frequently subjected

to axial tension, bending, and shear loadings as well as ous combinations of loading, as noted in Section 2.2 Con-crete piles must have adequate structural capacity for allmodes and combinations of loading that they will experi-ence For combined flexure and thrust loadings, the structur-

vari-al adequacy can be evvari-aluated more readily through the use ofmoment-thrust interaction diagrams and strength-designmethods

This section recommends provisions for ensuring that crete piles have adequate structural capacity based onstrength-design methods Recommendations are provided inSections 2.3.2, 2.3.4, and 2.3.5 for the direct use of strength-design methods Because of the historical use of allowablecapacities and stresses in piling design, however, recommen-dations are also provided for allowable axial service capaci-ties for concentrically loaded, laterally supported piles The

con-allowable service capacities P a recommended in Section

2.3.3 are intended specifically for cases in which the soil vides full lateral support to the pile and where the appliedforces cause no more than minor bending moments resultingfrom accidental eccentricities Piles subjected to larger bend-ing moments or with unsupported lengths must be treated ascolumns in accordance with ACI 318-95 and the provisionsgiven in Sections 2.3.2, 2.3.4, and 2.3.5 of this report.Foundation piles behave similar to columns, but there can

pro-be major differences pro-between the two regarding lateral port conditions and construction and installation methods.The piles to which the basic allowable stresses apply arefully supported laterally, whereas columns may be laterallyunsupported or sometimes supported only at intervals Thefailure mode of a column is due to structural inadequacy,whereas pile-foundation failures are caused by either inade-quate capacity of the pile-soil system (excessive settlement)

sup-or of the structural capacity of the pile A column is times a more critical structural element than an individualpile A column is an isolated unit whose failure would prob-ably cause collapse of that portion of the structure supported

some-by the column A single structural column, however, is often

supported by a group of four or more piles with the column

load shared by several piles

The structural design of the pile should consider both

tem-porary and permanent loads and stresses For example,

driv-ing stresses durdriv-ing pile installation (Section 2.2.1.2) can

govern the structural design of the pile Experience from

driving precast piles leads to a recommendation that the

min-imum concrete compressive strength f c should be 5000 lb/in.′ 2

(35 MPa) and that greater strengths are often necessary The

structural design of the pile should also consider the subsoil

conditions as they affect the magnitude and distribution of

forces within the pile

2.3.2 Strength design methods—The provisions for

strength design of concrete piles given herein were

devel-oped using strength design principles from ACI 318-95,

al-though no attempt has been made to completely follow the

column design requirements of ACI 318-95

The general strength design requirement for piling is that

the pile be designed to have design strengths at all sections

at least equal to the required strengths calculated for the

fac-tored loads determined using the loading factors and

combi-nations of service loading as stipulated in ACI 318-95

Section 9.2 The design strength of the pile is computed by

multiplying the nominal strength of the pile by a strength

re-duction factor φ, which is less than 1 The nominal strength

of the member should be determined in accordance with the

recommendations of ACI 318-95

The strength reduction factors φ recommended herein for

various types of loading conditions generally follow ACI

318-95, except that strength reduction factors for

compres-sion φc have been determined by the committee for the pile

member types not covered by ACI 318-95 Recommended

strength reduction factors for various forms of loading, as

well as additional recommendations, are provided in

Sec-tions 2.3.2.1 through 2.3.2.7 Further recommendations for

the use of the strength design method with piling are

provid-ed in Sections 2.3.4 and 2.3.5

2.3.2.1 Compressive strength—The recommended

compressive strength reduction factors φc for various types

of concrete piles are presented in Table 2.1 These reductionfactors have been determined based on consideration of con-struction experience and the different behaviors under loadsapproaching the failure loads for the various pile types Inaddition to the application of a strength reduction factor, allpiles subjected to compression shall be designed for the ec-centricity corresponding to the maximum moment that canaccompany the loading condition, but not less than an eccen-tricity of 5% of the pile diameter or width

The uncased concrete members (CIS piles), as a generalclass, cannot be inspected after placement of the concrete,and there have been many problems with penetration of thesurrounding soil into the pile section in some soil types andwith some construction techniques It is also uncertain towhat degree the reinforcement can be placed in its designedposition in a reinforced uncased pile The strength reductionfactor is a function of both the dimensional reliability of thecross section and dependence of the member strength on thestrength of the concrete actually attained in the member and

is set at 0.60 for uncased piles In some soil types, local perience may indicate that lower values of φ are prudent.Davisson et al (1983) provide an extensive discussion ofthese design factors

ex-2.3.2.2 Flexural strength—For concrete piles

subject-ed to flexure without axial load or flexure combinsubject-ed with ial tension, the strength reduction factor φt is 0.9 This valuecorresponds to the ACI 318-95 strength reduction factor forthese particular loading conditions For piles subjected toflexure combined with axial compression, the recommendedcompressive strength reduction factor φc given in Table 2.1should be used accordingly

ax-For reinforced concrete piles, prestressed concrete piles, orconcrete-filled pipe piles subjected to flexure and low values

of axial compression, the φ can be increased from the mended compression value φc to the value of 0.9 for flexurewithout axial load φt in accordance with the procedures given

recom-in Section 9.3.2 of ACI 318-95

2.3.2.3 Tensile strength—Concrete piles subjected to

axial tension (uplift) loads should be designed for the fulltension load to be resisted by the reinforcing steel (Section2.5) The strength reduction factor φt value used for this load-ing condition should be 0.9

2.3.2.4 Strength under combined axial and flexural

loading—The design and analysis of concrete piles, except

concrete-filled shell piles with confinement, that are

subject-ed to a significant bending moment in addition to axial forcesshould be done using moment-thrust interaction diagram in-formation developed in accordance with Chapter 10 of ACI318-95 The φ in Sections 2.3.2.1 and 2.3.2.2 of this reportand the loading factors and combinations in accordance withChapter 9 of ACI 318-95 should be used Under no circum-stances should the axial compression capacity exceed the ca-pacity corresponding to an eccentricity of 5% of the diameter

or width of the pile

Table 2.1—Recommended compressive strength

reduction factors φφφφc

Pile type

Compressive strength reduction factor φc

Concrete-filled shell, no confinement 0.65

Concrete-filled shell, confinement* 0.70

Uncased, plain or refinforced concrete† 0.60

Precast reinforced concrete or cast-in-place

reinforced concrete within shell 0.70

Pretensioned, prestressed reinforced concrete 0.70

* Shell of 14 gage minimum thickness (0.07474 in [1.9 mm]), shell diameter not over

16 in (400 mm), for a shell yield stress f ys of 30,000 lb/in.2 (210 MPa) minimum, f c′

not over 5000 lb/in 2 (35 MPa), noncorrosive environment, and shell is not designed

to resist any portion of axial load The increase in concrete strength due to

confine-ment shall not exceed 54%.

† Auger-grout piles, where concreting takes place through the stem of a hollow-stem

auger as it is withdrawn from the soil, are not internally inspectable The strength

reduction factor of 0.6 represents an upper boundary for ideal soil conditions with

high-quality workmanship A lower value for the strength reduction factor may be

appropriate, depending on the soil conditions, and the construction and quality

con-trol procedures used The designer has to carefully consider the reliable grout

strength, grout strength testing methods, and the minimum cross-sectional area of the

pile, taking into account soil conditions and construction procedures The addition of

a central reinforcing bar extending at least 10 ft (3 m) into the pile is recommended,

as this adds toughness to resist accidental bending and tension forces resulting from

other construction activities.

Many of the design aids for reinforced concrete columns

(CRSI 1996; ACI 1990) can also be used for the design of

piles to resist bending plus axial force Some adjustments,

however, are necessary to account for different values of φ

Fully understanding any assumptions made in the

prepara-tion of the design aids, especially the inclusion or exclusion

of the φ, is imperative PCI (1992, 1993) has published

de-sign data for pretensioned concrete piles, and a basic

approach to the calculation of moment-thrust interaction

re-lationships is given by Gamble (1979)

The assumptions made for the analysis of concrete-filled

pipe are worthy of noting For the analysis of concrete-filled

pipe under combined bending and compression, it can be

as-sumed that there is adequate bond between the concrete and

the pipe so that the strains in concrete and steel match at the

interface This assumption cannot be universally true; for

ex-ample, at sections near the ends of the pipe, the quality of

bond can vary, and judgment must be used by the engineer

The concrete compression failure strain can be taken as

0.003 The pipe wall can be modeled either as a continuous

tube or as a number of discrete areas of steel evenly spaced

around the perimeter of the section The pipe wall can act as

tension or compressive reinforcement, but it cannot act as

confinement reinforcement at the same time The assumption

of adequate bond is reasonable in this case, but it is not

fea-sible when considering loading in a case where the objective

is to anchor a major tension force into the concrete piling in

a permanent structure Shear connectors or other positive chorage are required in this scenario

an-For the case in which a concrete-filled shell is counted onfor confinement, the shell is effective in increasing the con-centric compression capacity but adds nothing to the bendingcapacity, which significantly increases the sensitivity of themember to eccentricity of load If it is necessary to constructthe moment-thrust interaction diagram to address eccentrici-ties for concrete-filled shell piles with confinement, con-structing the interaction diagram by the procedures inDavisson et al (1983) is recommended

2.3.2.5 Shear strength—Piles that have significant

bending moments will often have significant shear forces.Provisions in Chapter 11 of ACI 318-95 should be followedwhen designing shear reinforcement Special attention is re-quired when piles have both significant tension and signifi-cant shear forces A strength reduction factor of 0.85 should

be used for shear in reinforced concrete piles, prestressedconcrete piles, and pipe piles For nonreinforced piles, thestrength reduction factor for shear used should be 0.65

2.3.2.6 Development of reinforcement—Development

of stress in embedded reinforcement (bond) should spond to the information given in Chapter 12 of ACI 318-95

corre-2.3.2.7 Prestressed piles—Prestressed piles designed

by strength-design methods also require serviceabilitychecks to ensure that their service load behavior is adequate,

in addition to the limiting capacities found through strengthdesign These serviceability checks should be performed inaccordance with the recommendations in Section 2.3.3.3 ofthis report

2.3.3 Allowable axial service capacities for concentrically

loaded, laterally supported piles—Equations for the

allow-able axial compressive service capacity can be developed fordifferent types of concrete foundation piles by consideringthe recommended compressive strength reduction factors in

Section 2.3.2.1, a minimum eccentricity factor, and a bined average load factor

com-The eccentricity factor is a function of the pile tional shape (octagonal, round, square, or triangular) forplain concrete piles For a reinforced concrete pile, the ec-centricity factor is also a function of the reinforcing steelratio, the location of the reinforcement within the cross sec-tion and the concrete and steel strengths The eccentricityfactor for a particular pile section can be determined from itsnominal strength interaction diagram as the ratio of the nom-inal axial strength at a 5% eccentricity to the nominal axialstrength under concentric loading The allowable axial ser-vice capacity equations in Table 2.2 are based on eccentricityfactors taken from a Federal Highway Administration report(Davisson et al 1983) and a PCA report (PCA 1971) inwhich the general shapes of moment-axial force interactiondiagrams for various types of piles were studied in detail.The combined average load factor should be computed asthe ratio of the factored load to the service load The allow-able axial service capacity equations in Table 2.2 assume acombined average load factor of 1.55, based on an average

cross-sec-of the ACI 318-95 load factors for dead and live load ing the dead load is equal to live load), which is generally a

(assum-Table 2.2—Allowable service capacity for piles with

negligible bending *

Pile type Allowable compressive capacity

Concrete-filled shell, no confinement P a = 0.32f c′A c

Concrete-filled shell, confinement† P a = 0.26( f c′ + 8.2t shell f ys /D)A c

≤ 0.4f c′A c

Uncased plain concrete‡ P a = 0.29f c′A c

Uncased reinforced concrete§,|| P a = 0.28f c′A c + 0.33f y A st

Precast reinforced concrete or

cast-in-place reinforced concrete within

shell§,||

P a = 0.33f c′A c + 0.39f y A st

Pretensioned, prestressed concrete§,|| P a = A c (0.33f c′ – 0.27f pc)

Concrete-filled steel pipe P a = 0.37f c′A c + 0.43f yp A p

* Based on an eccentricity of 5% of pile diameter or width, and an assumed average

load factor of 1.55 In cases of very high live or other loadings such that the average

load factor exceeds 1.55, the allowable capacity equations should be reduced

accord-ingly.

† Shell of 14 gage minimum thickness (0.0747 in [1.9 mm]), shell diameter not over

16 in (400 mm), for a shield yield stress f ys of 30,000 lb/in.2 (210 MPa) minimum, f c′

not over 5000 lb/in.2 (35 MPa) noncorrosive environment, and shell is not designed to

resist any portion of axial load The allowable load P a shall not exceed 0.40f c′ A c .

‡ Auger-grout piles, where concreting takes place through the stem of a hollow-stem

auger as it is withdrawn from the soil, are not internally inspectable The strength

reduction factor of 0.6, on which the strength coefficient of 0.29 is based, represents

an upper boundary for ideal soil conditions with high-quality workmanship A lower

value for the strength reduction factor may be appropriate, depending on the soil

con-ditions and the construction and quality control procedures used The designer has to

carefully consider the reliable grout strength, grout strength testing methods, and the

minimum cross-sectional area of the pile, taking into account soil conditions and

con-struction procedures The addition of a central reinforcing bar extending at least 10 ft

(3 m) into the pile is recommended, as this adds toughness to resist accidental bending

and tension forces resulting from other construction activities.

§ Applicable if the longitudinal steel cross-sectional area is at least 1.5% of the gross

pile area, and at least four symmetrically placed reinforcing bars are supplied, with six

bars preferred.

|| An eccentricity factor of 0.86 has been assumed for reinforced concrete piles For

reinforced concrete piles with a concrete strength, f c′, less than 5000 lb/in.2 (35 MPa),

or for piles with axial reinforcement areas (as a percentage of the gross pile area)

greater than 3% for round piles or greater than 4.5% for square piles, the eccentricity

factor should be evaluated from a nominal strength moment-thrust interaction diagram

and the allowable capacity equation adjusted accordingly.

Table 2.4—Values for K for various head and end conditions *

Head condition End conditions

Both fixed One fixed Both hinged

conservative assumption If the controlling loading case is

dominated by very high live or other loadings, such that the

actual average load factor exceeds 1.55, the allowable

ca-pacity equations indicated herein should be reduced

accord-ingly

The allowable axial compressive service capacity

equa-tions given in this report are specifically restricted to cases

in which the soil provides full lateral support to the pile and

where the applied forces cause no more than minor bending

moments (resulting from accidental eccentricity) Piles

sub-jected to larger bending moments or with unsupported

lengths must be treated as columns in accordance with ACI

318-95 and the provisions in Sections 2.3.2, 2.3.4, and 2.3.5

of this report

2.3.3.1 Concentric compression—The allowable axial

compressive service capacity for laterally supported solid

concrete piles can be determined by the equations given in

Table 2.2 These equations were developed based on the

pro-cedures described in Section 2.3.3 and correspond to a

nom-inal factor of safety (ratio of the average load factor to the

strength reduction factor) that ranges from approximately

2.1 to 2.6, depending on the pile type Hollow piles and piles

with triangular cross sections must be analyzed and designed

using a moment-axial force interaction design method, with

a minimum eccentricity of 5% of the pile diameter or width,

as described in Section 2.3.2

2.3.3.2 Concentric tension—Concrete piles subjected to

axial tension (uplift) loads are designed for the full tension

load to be resisted by the steel (Section 2.5) The allowable

tension service capacity for reinforcing steel is

(2.1)

P at = 0.5f y A st

For prestressed concrete piles where the full tension load is

to be resisted at the pile head by unstressed strands extendedinto a footing or cap, the allowable tension service capacity is

(2.2)

2.3.3.3 Special considerations for prestressed piles—

Prestressed piles must have serviceability checks applied toensure that their service-load behavior is adequate, in addition

to the limiting capacities described in Section 2.3.2 Theallowable service-load stress limits given in Table 2.3 should

be determined using concrete compressive strengths f′c sponding to the age of the concrete under consideration

corre-2.3.4 Laterally unsupported piles—That portion of the

pile that extends through air, water, or extremely soft soil(Prakash and Sharma 1990) should be considered unsupport-

ed and designed to resist buckling under the imposed loads(Section 2.1.6) The effects of length on the strength of pilesshould be taken into account in accordance with Sections10.10 and 10.11 to 10.13 of ACI 318-95 Whereas Sections

10.11 to 10.13 give an approximate method suitable for Kl u /r

< 100, Section 10.10 describes the requirements for a nal analysis of the effects of length

ratio-The effective pile length l e is determined by multiplying

the unsupported structural pile length l u by the appropriate

value of the coefficient K from Table 2.4 or from Chapter 10

of ACI 318-95 For cases in which the top of the pile is free

to translate, the coefficient K requires careful consideration

and should exceed 1.0

The unsupported portion of a foundation pile is an sion of the laterally supported portion, which can be severaltimes longer than the unsupported portion Thus, such a pile

exten-is deeply embedded for its lower length and at some depthbelow the ground surface could be considered to be fixed.Achieving complete end fixity for a building column is dif-ficult Furthermore, for many structures using unsupportedpile lengths, the pile tops are framed into the structure muchmore heavily than most building columns with a greater re-sulting end fixity at the top For shallow penetrations, the pilepoint should be considered hinged unless test data provesotherwise

If the structural length l u of an unsupported concrete pile

is not confined in a steel pipe or shell with a minimum wallthickness of 0.1 in (2.5 mm) or spirally reinforced, the ca-

P at = 0.1f pu A ps

*Units for allowable stresses and f′c in the equations in this table are lb/in.2 (1 lb/in.2

= 0.0069 MPa) Because the tension stresses are a function of the square root of f′c if

other units are used for f′c it is also necessary to change the coefficients in front of the

radical Conversions for the equations are:

Equation in terms of lb/in.2 Equation in terms of MPa

3√f′c (√f′c) /4

6√f′c (√f′c) /2

†In piles that are expected to be subjected to tension, the ultimate capacity of the

pre-stressing steel should be equal to or greater than 1.2 times the direct tension cracking

force, unless the available strength is greater than twice the required factored ultimate

tension load; that is, f ps A ps ≥ 1.2 (fpc + 7.5 √f′c )A c , f pc , and f ps are in lb/in 2 units.

* For piles doweled to the cap, the degree of fixity at the doweled end could range from

50 to 100% depending on the embedment of the pile into the cap, the design of the eled connection, and the resistance of the structure to translation and rotation For fixed

dow-ends the values of K are based upon complete fixity and should be adjusted depending

on the actual degree of fixity (Davisson 1970b; ACI 318-95; Joen and Park 1990, PCI 1993.)

pacity determine on the basis of strength design should be

re-duced by 15%

The structural length l u as defined here is the unsupported

pile length between points of fixity or between hinged ends

For a pile fixed at some depth L s below the ground surface,

the structural length l u would be equal to the length of pile

above the ground surface L u plus the depth L s

(2.3)

The depth below the ground surface to the point of fixity L s

can be estimated by Eq (2.4) for preloaded clays, or by Eq

(2.5) for normally loaded clay, granular soils, silt, and peat

(2.4)

(2.5)

The total length of the portion of the pile embedded in the

soil must be longer than 4R or 4T for this analysis to be valid;

otherwise, a more detailed analysis is required Furthermore,

the unsupported length above ground must be greater than 2R

(that is, L u > 2R) or T (that is, L u > T) for Eq (2.4) and (2.5)

to be valid In most practical cases, the unsupported length

above ground L u will be greater than 2R or T For cases

where the L u value does not satisfy the restrictions on Eq

(2.4) and (2.5), modifications of the coefficients in these

equations are required (Davisson and Robinson 1965;

Prakash and Sharma 1990)

The horizontal subgrade modulus k is approximately 67

times the undrained shear strength of the soil (k = 67s u) It is

assumed to be constant with depth for preloaded clay and

vary with depth for normally loaded clay The value of the

coefficient of horizontal subgrade modulus n h for normally

loaded clay is equal to k divided by the depth and can be

approximated by the best triangular fit (slope of line through

the origin) for the top 10 to 15 ft (3 to 4.5 m) on the

k-versus-depth plot (Davisson 1970b) Representative values of the

coefficient of horizontal subgrade modulus n h for other soils

are shown in Table 2.5 These values also apply to

sub-merged soils

2.3.5 Piles in trestles—For piles supporting trestles or

ma-rine structures that could occasionally receive large

over-loads, the capacities determined on the basis of strength

design (Section 2.3.2) or the allowable service capacities

de-termined in Section 2.3.3 should be reduced by 10 % The

ca-pacity is reduced further by a reduction factor depending on

both the l u /r ratio and the head and end conditions (Section

2.3.4) For unsupported piles not spirally reinforced, a further

15% reduction in capacity is recommended (Section 2.3.4)

2.3.6 Seismic design of piles—In areas of seismic risk,

de-signing piles or other structural members on the basis of

strength alone is not adequate These members must also

possess adequate ductility, and more importantly, ductility

de-in such an analysis can lead to unrealistically large curvatureand rotation requirements for the piles

Most reinforced and prestressed concrete structural bers have some inherent ductility, but this is often inadequatefor seismic response and analysis purposes unless specialmeasures are taken to enhance it Ductility is a function ofmany factors It will decrease if the area of tensile reinforce-ment, its yield strength, or both, are increased; if the axialcompression force acting on a pile or column is increased; or

mem-if the concrete strength is decreased Ductility will increase mem-ifcompression reinforcement is added, if the concrete strength

is increased, if the axial compression force is decreased, or ifthe compression zone of the member is provided with con-finement reinforcement The most common example of con-finement reinforcement is the spiral required in spirallyreinforced concrete columns according to Eq (10-6) of ACI318-95, often referred to as an ACI Spiral Experience frompast earthquakes and from laboratory tests demonstrates thatthis spiral provides significant ductility in flexural modes,and that it also provides a major shear-strength contribution.Although this spiral leads to ductile members, the selection ofthe spiral ratio and bar area and spacing is unrelated to flex-ural or shear requirements but rather is related to axial com-pression considerations Major improvements in ductility can

be obtained with lighter spirals than the ACI Spiral Becausethe requirement was explicitly derived for circular spirals, itdoes not address the requirements for square or rectangularlongitudinal reinforcement arrangements Other more empir-ical expressions have been developed for these cases.This report does not recommend the use of the ACI Spiral

in foundation piles for purposes of achieving flexural ity, but the requirements are repeated here to provide a basis

ductil-Table 2.5—Values of n h

Soil type n h, lb/in.3 kN/m3

Sand* and inorganic silt

of comparison with recommendations that follow Eq 10-6

of ACI 318-95 is expressed, with slightly modified notation,

in Eq (2.6)

(2.6)

where

f′c = compressive strength of concrete;

f yh = yield stress of spiral reinforcement;

A g = gross area of member cross section; and

A core = area of core of section, to outside diameter of the

spiral

The spiral steel ratio ρs is a volume ratio relating the

vol-ume of steel in the spiral to the volvol-ume of concrete contained

within the spiral

(2.7)

where

A sp = area of wire or bar used in spiral;

d core = diameter of core of section to outside diameter of

spiral; and

s sp = spacing or pitch of spiral along length of member

Although an ACI Spiral provides excellent ductility, it is

extremely difficult to provide the resulting amount of spiral

reinforcement in many practical cases, such as square piles

with longitudinal reinforcement arranged in a circular

pat-tern This difficulty arises because the area ratio A g /A core is

unfavorable for square members containing round spirals

and becomes especially unfavorable for small members

High concrete strengths also lead to large steel ρs

require-ments It is not desirable to have the pitch too small because

it makes concrete placement very difficult during

manufac-turing Also, as the pitch becomes smaller, there is an

in-creased tendency for the concrete cover outside of the

closely spaced spiral to spall off during pile-driving

opera-tions

The ACI Spiral has been widely adopted for use in the

de-sign of building columns and bridge piers to resist major

seismic forces and deformations where the goal is to provide

flexural ductility For example, the ACI Spiral is used in

Chapter 21 of ACI 318-95 with a lower limit to ACI

318-95 Eq (10-6) of

(2.8)

The minimum ρs requirement of Eq (2.8) governs when the

ratio of A g /A core becomes less than approximately 1.27,

which occurs only in large columns

Although the ACI Spiral is widely adopted for column

de-sign, its adoption for piling is less universal For example,

the Uniform Building Code (1994) adopts the ACI Spiral but

limits the spiral steel ratio so that it need not be larger than

ρs = 0.12 f′c /f yh for nonprestressed concrete piling in zones ofhigh seismic risk

The PCI Committee on Prestressed Concrete Piling (1993)recommends minimum spiral steel ratios for members withround steel patterns and minimum steel areas for memberswith square steel arrangements for regions of high seismicrisk These recommendations are repeated herein and are en-dorsed by ACI Committee 543 for application to both pre-stressed and reinforced concrete piling in regions whereseismic resistance is required The terms used herein to de-scribe seismic risk (low, moderate, and high) are used in thesame context as these terms are used in Chapter 21 of ACI318-95

2.3.6.1 Regions of low to moderate seismic risk—

In regions of low to moderate seismic risk, lateral ment should meet the following steel ratio

reinforce-(2.9)

with two limits on materials

f′c ≤ 6000 lb/in.2 (40 MPa); and

f yh≤ 85,000 lb/in.2 (585 MPa)

2.3.6.2 Regions of high seismic risk—In regions of

high seismic risk, the following minimum amounts of finement reinforcement are recommended:

con-• Reinforcement of circular ties or spiral

(2.10)

but not less than

(2.11)

where

P u = factored axial load on pile;

and with two limits on materials

f′c ≤ 6000 lb/in.2 (40 MPa); and

=

but not less than

(2.13)

where

h c = cross-sectional dimension of pile core measured

cen ter-to-center of spiral or tie reinforcement and with

the limit that

f yh ≤ 70,000 lb/in.2 (480 MPa)

The formats of the equations for high seismic risk

re-gions, but not the numerical constants, follow research

con-ducted in New Zealand (Joen and Park 1990) and the New

Zealand Standard Code of Practice for the Design of

Con-crete Structures (1982)

2.3.6.3 Needed research—Most of the reversed

bend-ing tests of piles have been conducted on octagonal

preten-sioned members (Banerjee et al 1987) Other tests, including

tests of square members with round and square

reinforce-ment patterns and round members of both reinforced and

pre-stressed concrete are needed, along with supporting

analytical work These tests should include a full range of

confinement reinforcement ratios or areas, and should

in-clude tests with and without axial loads Both solid and

hol-low members should be considered In addition to studies of

the rotation capacities that are possible from various

mem-bers, studies of the rotational demands or requirements that

can be imposed by the supported structure with various soil

profiles are needed

2.3.6.4 Vertical accelerations—Experience from the

1994 Northridge earthquake in California reveals that at and

near the epicenter, vertical accelerations approached the

magnitude of horizontal accelerations This is significant

be-cause accelerations on the order of 1.0 g were recorded The

ramifications of high vertical accelerations should be

consid-ered by the structural engineer relative to piling because

se-vere axial overloading of piles can occur under earthquake

conditions In geographic areas where high vertical

accelera-tions are possible, it may be advisable to consider another

case of loading that codes do not now consider, namely,

nor-mal service axial load plus that produced by an earthquake

2.4—Installation and service conditions affecting

design

Several installation conditions can affect the overall

pile-foundation design and the determination of pile capacity

Some of these relate to installation methods, equipment, and

techniques (Chapter 5) Others relate to the subsoil

condi-tions or the qualificacondi-tions of the pile contractor Obviously,

the engineer cannot allow for all contingencies in his design

but many can be provided for by proper analysis of subsoil

data, preparation of competent specifications, use of

quali-fied contractors, and adequate inspection of the work

2.4.1 Pile-head location tolerances—Some tolerance

should be allowed between the as-installed position of the

pile head and the required plan location Deviations from the

plan pile-head locations can be caused by: survey errors;

equip-or by general ground movements after the piles have beendriven caused by embankment pressures, construction oper-ations, or other surcharge loads

The deviation that should be allowed varies with the pileload and group size A smaller tolerance is required for a sin-gle pile carrying a very high load A larger tolerance can beallowed for a large group of piles under a structural mat Atolerance of 3 in (75 mm) in any direction is reasonable fornormal pile usage Marine work and large piles may requirelarger tolerances

Generally, an overload of 10% on a pile due to deviation

of the pile location does not require modifying the pile cap orgroup If this overload is exceeded, additional piles should beinstalled (and where necessary the pile cap modified) so thatthe center of gravity of the group remains substantially underthat of the load

Sometimes piles driven off location can be pulled orpushed back into plan location, but this practice is not recom-mended If this practice is permitted, the force used to movethe pile into proper position should be limited and carefullycontrolled according to a lateral load analysis, consideringthe type and size of pile and the soil conditions This is espe-cially critical for precast piles used for trestle structureswhere a long moment arm can result in structural damage tothe pile even with relatively low forces (Section 5.3.5)

2.4.2 Axial alignment tolerances—Deviations from

quired axial alignment can result from the pile driven off quired alignment but with its axis remaining straight, the piledriven with its axis not on a straight line from pile head to tip,

re-or a combination of these two with the pile bent and the tipoff its plan location Deviations from a straight line axis cantake the form of a long sweeping bend or a sharp bend called

a dogleg

The deviation of the pile axis from the specified ment, whether vertical or battered, should be within the fol-lowing tolerances:

align-• Two percent for embedded piles driven through sandysoils or soft clays;

• Four percent for embedded piles driven through cult soils of nonuniform consistency, boulder-riddensoils, or batter piles driven into gravel; and

diffi-• A maximum of 2% of the total pile length in marinestructures that have over half the pile length in waterrather than soil

Piles driven outside of these tolerances should be reviewed

by the engineer The review should include consideration ofhorizontal forces and interference with other piles and mayrequire review of the pile cap

For axial deviations from a straight line (bent piles), theallowable tolerance could range from 2 to 4% of the pilelength, depending on subsoil conditions and type of bend,which could be sharp (excluding breaks in the pile) or sweep-ing bends of varying radii Experience and load tests havedemonstrated that, in most cases, the passive soil pressures

are sufficient to restrain the pile against the bending stresses

that can develop For severely bent piles, the capacity can be

analyzed by soil mechanics principles or checked by load

test When axial alignment cannot be adequately measured

for driven piles, the tolerances should be more conservative

2.4.3 Corrosion—The pile environment should be

care-fully checked for possible corrosion of either the concrete or

the load-bearing steel Corrosion can be caused by direct

chemical attack (for example, from soil, industrial wastes, or

organic fills), electrolytic action (chemical or stray direct

currents), or oxidation

When the pile is embedded in natural soil deposits (not

recently placed fills), corrosion due to normal oxidation is

generally not progressive and frequently very minor The

presence of corrosive chemicals or destructive electric

cur-rents should be determined and the proper precautions taken

Soils and water with high sulfate contents require special

precautions to ensure durability (Chapter 3)

Under detrimental corrosive environments, exposed

load-bearing steel should be protected by coatings, concrete

encasement, or cathodic protection Concrete can be

protect-ed from chemical attack by using special cements, very rich

and dense mixtures, special coatings, and sometimes by

us-ing steel encasement Fiberglass jackets have also been used

Pile splices may require special treatment to ensure that their

corrosion resistance is adequate

2.4.4 Splices—Precast piles are usually designed and

con-structed in one piece; however, field splices may be needed

if the lengths are misjudged In the cases of very long piles,

those long enough to make manufacture, transport, and

han-dling inconvenient field splices will be part of the original

design Some piles have standard stock lengths and splicing

is a part of their normal manufacture and usage (sectional

precast piles) These sectional piles can also be mandated by

headroom limitations at the pile locations or by the limits of

the contractor’s equipment The engineer should exercise

control over the use of or need for pile splices through their

choice of pile types and preparation of specified installation

requirements

Splices driven below the ground surface should be

de-signed to resist the driving forces and the service loads with

the same factor of safety as the basic pile material

Above-ground splices and built-up pile sections should be designed

to develop the required pile strength for the imposed loads

(and also driving forces if they are to be driven after splicing)

Splices may need to be designed to resist the full

compres-sion, bending, and tension strength of the body of the pile

Torsional strength can be a consideration in some cases The

potential for corrosion should be considered when selecting

final locations for splices Special protective sleeves or other

protective means may have to be provided when the pile

splice will be exposed to seawater or other severe corrosion

hazards Bruce and Hebert (1974a, 1974b), Gamble and

Bruce (1990), and Venuti (1980) report on the behavior of

several different splices, and also discuss many other splices

that may be available

For the detailed design of the splice, several different

crit-ical sections and different failure modes should be

consid-ered For instance, if the splice involves dowels (in anyform), the most critical section could be either at the ends ofthe sections being joined or at the ends of the dowel bars Thecapacity could be governed by either the pile strength, splicestrength, or bond capacities of either the dowels or the pilereinforcement The bond problem will be especially severefor pretensioned piles, and the dowels must extend the fulldevelopment length of the strand

Many specific requirements can be placed on mechanicalsplices, including:

• Ends of segments should be plane and perpendicular tothe pile axis;

• Splices should have a centering device;

• Splices should be symmetrical about axis of member;and

• Locking and connection devices should be designedand installed to prevent dislodgement during driving.Adequate confinement reinforcement should be provided

in the splice region Dowel bars that are embedded in the pile

as part of the splice mechanism may need to have staggeredcutoff points rather than all ending at the same section.Dowel splices should have oversized grout holes to permiteasy and complete filling of the holes The holes can beeither drilled or cast

2.4.5 Relaxation and soil freeze—If soil relaxation or

freeze can occur, the final penetration resistance duringinitial driving of the pile is generally not an indication of theactual pile static capacity In such cases, dynamic methods ofcapacity prediction (Sections 2.1.2.3, 2.1.2.4, and 2.1.2.5)

will not produce valid results without modifications based on

a load test or redriving results Relaxation is evidenced by areduction in the final penetration resistance after initial driv-ing and could be accompanied by a loss of bearing capacity.Soil freeze has the opposite effect on pile capacity and isassociated with regain of strength of soils after being dis-turbed during the driving process with a corresponding in-crease in the bearing capacity

The possibility of these phenomena should be recognized

by the designer when establishing such requirements as type

of pile, pile length, and driving resistance Relaxation can bechecked by redriving some piles several hours after initial fi-nal driving to determine if the driving resistance has beenmaintained Soil freeze can also be checked by redriving, butload testing is more positive Sufficient time should beallowed before testing to permit the soil strength to be re-gained This required time could range from a few hours to

as long as 30 days Retapping of piles produces more validinformation if the hammer-cushion-pile system is the same

as for initial driving

2.4.6 Compaction—Many soils are compacted and

densi-fied through the process of pile driving, especially when placement-type piles are installed without pre-excavationsuch as jetting or predrilling The soil strength properties areusually increased, although the extent and degree to whichthey will increase are not easy to predict Compaction is usu-ally progressive as more piles are driven within a group In-stallation sequence or methods should be controlled to

dis-prevent extreme variations in pile lengths due to ground

compaction (Sections 5.1.6 and 5.1.7)

2.4.7 Liquefaction—Liquefaction is usually associated

with earthquake or large vibratory forces combined with

liquefiable granular soils This can result in loss of pile

ca-pacity Although it is not generally necessary to consider this

in normal pile foundation design, it is necessary to consider

liquefaction in seismically active regions Liquefaction that

causes vertical ground movements will cause downdrag and

possible settlement of friction piles Piles in slopes can be

subjected to large lateral loads and displacements due to

liq-uefaction If this phenomenon must be provided for, the

pile-soil capacity should be developed below the zone of possible

soil liquefaction Liquefaction generally does not occur

be-low a depth of 30 ft (9 m) and, at most, 50 to 60 ft (15 to 18

m) Further, it is not likely to occur within a pile group

be-cause of the soil compaction resulting from the pile driving

It can, however, occur around the perimeter of a pile group;

therefore, under these conditions, the stability of the group

should be evaluated Methods of determining whether soils

at a particular site can experience liquefaction (Kriznitsky et

al 1993; Ohsaki 1966; Poulos et al 1985; Seed et al 1983)

should be used whenever there is significant seismic activity

Some soils exhibit temporary liquefaction during pile driving

with corresponding reduction in penetration resistance The

establishment of the soil resistance can be detected by

re-driving the pile, but under severe conditions where rere-driving

immediately creates liquefaction, the capacity of the pile

may have to be determined by static load testing

2.4.8 Heave and flotation—Pile heave is the upward

movement of a previously driven pile caused by the driving

of adjacent piles The designer should be alert to possible pile

heave, include provisions in the specification to check for

this phenomenon, and take precautionary measures Heave

of friction piles may have no detrimental effect on pile-soil

capacity, but it can affect the structural capacity of the pile if

it is weak in tension

Heave can take place when driving piles through upper

co-hesive soils that do not readily compress or consolidate

dur-ing drivdur-ing Under severe conditions, heave is quite evident

from the upward movement of the ground surface When

heave conditions exist, elevation checks should be taken on

the tops of the driven piles Such level readings can be taken

on the tops of pile casings that cannot stretch For laterally

corrugated pile shells, check levels should be made on pipe

telltales bearing on the pile tips, because heave that causes

only shell stretch should not affect the pile capacity

Heave can often be limited or even eliminated by pile

pre-excavation or increasing the pile spacing The shells for CIP

concrete piles should be left unfilled until the pile-driving

operation has progressed beyond the heave range CIS

con-crete piles and sectional concon-crete piles having joints that

can-not take tension should can-not be used under heave conditions

unless positive measures are taken to prevent heave

If pile heave occurs, the unfilled shells or casings for CIP

concrete piles and most precast concrete piles can be redriven

to compensate for heave CIS concrete piles containing

full-length reinforcement can be subjected to a limited amount of

redriving to reseat the pile CIS concrete piles without nal reinforcement should be abandoned if heaved Sectionalprecast concrete piles having slip-type joints can be redriven

inter-to verify that they are sound and that the joints are closed Inthe case of sectional piles, however, all of the heave should

be considered to have occurred at a single joint and the jointshould not have been opened completely as a result of pileheave If necessary, CIP piles can be redriven to compensatefor heave after the shell is filled with concrete, if proper tech-niques are used A wave-equation analysis can be used to aid

in the design of the hammer-cushion combination requiredfor such redriving

Flotation can occur when pile shells or casings are driven

in fluid soils and a positive buoyancy condition exists Checkelevations should be made as for heave, and the piles redriven

if required It may be necessary to create negative buoyancy

or use some means to hold the piles down until the casingsare filled with concrete

2.4.9 Effect of vibration on concrete—This is usually a

consideration in installing CIP concrete piles using a steelcasing or shell Pile installation is done in two separate oper-ations, driving the shell and filling it with concrete Usuallythe concreting operation follows closely behind the driving,provided that the vibrations do not damage the fresh con-crete Tests have indicated that pile-driving vibration duringthe initial setting period of concrete has no detrimental effect

on the strength of the pile (Bastian 1970) The minimum tance between driving and concreting operations, however,

dis-is often specified as 10 to 20 ft (3 to 6 m) (Davdis-ission 1972b;Fuller 1983) When a minimum distance is not specified, it isgenerally satisfactory if one open pile remains between thedriving operation and a concreted pile or if the minimum dis-tance is 20 ft (6 m), whichever is less When ground heave orrelaxation is occurring, however, the concreting operationshould not be closer to pile driving than the heave range orthe range within which redriving is required

The sequence of installation of CIS concrete piles should

be controlled in a manner to prevent damage to freshlyplaced concrete by the driving or drilling of adjacent piles.This frequently precludes the installation of adjacent piling

on the same day as a means of preventing ground ments that could harm the immature concrete

displace-2.4.10 Bursting of hollow-core prestressed piles—Internal

radial pressures in both open-ended and close-ended hollowprecast piles lead to tension in the pile walls and can causebursting of such piles These radial pressures can result fromdriving or installation conditions, such as use of internal jets,water-hammer effects, lateral soil plug pressures, or concretepressures if filled after installation They can also developunder service conditions such as gas pressure buildup fromdecomposition of core form materials, or ice pressure fromfreezing of free water in the core The potential effects ofsuch internal pressures should be evaluated during the design

of such piles (Sections 4.2.5 and 5.2.1.5)

2.5—Other design and specification considerations

The pile-foundation design should include other ations that may relate to specific type piles or that may have

consider-to be covered in the plans and specifications consider-to ensure that

piles are installed in accordance with the overall design

Some of these considerations are closely tied to items

dis-cussed in Chapters 4 and 5

2.5.1 Pile dimensions—Usually the minimum acceptable

diameter or side dimension for driven piles is 8 in (200

mm) Except for auger-injected piles and drilled and grouted

piles, drilled piles are usually a minimum of 16 in (400 mm)

di-ameter If construction or inspection personnel must enter the

shaft, however, the diameter should be at least 30 in (760

mm)

2.5.2 Pile shells—Pile shells or casings driven without a

mandrel should be of adequate strength and thickness to

withstand the driving stresses and transmit the driving energy

without failure Proper selection can be made with a

wave-equation analysis Pile shells driven with a mandrel should

be of adequate strength and thickness to maintain the

cross-sectional shape and alignment of the pile after the mandrel is

withdrawn

Corrugated shells are not considered to carry any axial

de-sign load To be considered as load bearing, plain or fluted

casings should be a minimum of 0.10 in (2.5 mm) thick and

have a cross-sectional area equal to at least 3% of the gross

pile section

2.5.3 Reinforcement—Reinforcement will be required in

concrete piles primarily to resist bending and tension

stress-es, but can be used to carry a portion of the compressive

load For bending, reinforcement consists of longitudinal

bars with lateral ties of hoops or spirals When required for

load transfer, the main longitudinal bars are extended into

the pile cap, or dowels are used for the pile-to-cap connection

The extent of reinforcement required at any section of the

pile will depend on the loads and stresses applied to that

sec-tion (Sections 2.2 and 2.3) Longitudinal bars used to carry a

portion of the axial load can be discontinued along the pile

shaft when no longer required because of load transfer into

the soil, but not more than two bars should be stopped at any

one point along the pile

2.5.3.1 Reinforcement for precast concrete piles—

Pile beam-column behavior is determined, to a great extent,

by the reinforcement ratio A lightly reinforced section, with

approximately 0.5% steel, will have approximately the same

cracking and yield moments, implying an extremely large

reduction in stiffness after cracking leading to imminent

col-lapse At 1.0% steel, the yield moment would be more than

twice the cracking moment, but the decrease in stiffness

af-ter cracking is still important At 1.5% longitudinal steel

content, the yield moment will be 3.5 to 4 times the cracking

moment and the loss of stiffness at cracking is less

impor-tant Piles with less than 1.5% steel have been used

success-fully in some soil conditions, but great care is required in

handling, transportation, and driving to avoid damage due to

excessive bending stresses The loss of stiffness at cracking

can be extremely important for a pile in which column

length effects become important, such as in piles extending

through air or water Because of this behavior, the

commit-tee recommends reinforced concrete piles that are driven to

their required bearing values have a longitudinal steel

cross-sectional area not less than 1.5% nor more than 8% of thegross cross-sectional area of the pile If after a thorough anal-ysis of the handling, driving, and service-load conditions, thedesigner selects to use less than 1.5% (of gross area) longitu-dinal steel, such use should be limited to nonseismic areas

At least six longitudinal bars should be used for round or tagonal piles, and at least four bars for square piles

oc-Longitudinal steel should be enclosed with spiral ment or equivalent hoops Lateral steel should not be smallerthan W3.5 wire (ACI 318-95 Appendix E) and spaced notmore than 6 in (150 mm) on centers The spacing should becloser at each end of the pile

reinforce-2.5.3.2 Reinforcement for precast prestressed piles—

Within the context of this report, longitudinal prestressing isnot considered as load-bearing reinforcement Sufficient pre-stressing steel in the form of high-tensile wire, strand, or barshould be used so that the effective prestress after losses issufficient to resist the handling, driving, and service-loadstresses (Section 2.5.3.3) Post-tensioned piles are cast withsufficient mild steel reinforcement to resist handling stressesbefore stressing

For pretensioned piles, the longitudinal prestressing steelshould be enclosed in a steel spiral with the minimum wiresize ranging from W3.5 to W5 (ACI 318-95 Appendix E),depending on the pile size The wire spiral should have amaximum 6 in (150 mm) pitch with closer spacing at eachend of the pile and several close turns at the tip and pile head.The close spacing should extend over at least twice the diam-eter or thickness of the pile, and the few turns near the endsare often at 1 in (25 mm) spacing

Occasionally, prestressed piles are designed and structed with conventional reinforcement in addition to theprestressing steel to increase the structural capacity and duc-tility of the pile This reinforcement reduces the stresses inthe concrete and should be taken into account

con-2.5.3.3 Effective prestress—For prestressed concrete

piles, the effective prestress after all losses should not be lessthan 700 lb/in.2 (4.8 MPa) Significantly higher effectiveprestress values are commonly used and may be necessary tocontrol driving stresses in some situations (see Item J in Sec-tion 5.2.2 for additional comments on the use of higher effec-tive prestress values)

2.5.3.4 Reinforcement for CIP and CIS concrete

piles—Except for pipe and tube piles of adequate wall

thick-ness that are not subject to detrimental corrosion, ment is required in CIP and CIS concrete piles for anyunsupported section of the pile and when uplift loads arepresent Reinforcing will also be required for lateral loading,except for very small lateral loads under conditions wherethe presence of concurrent axial compression loads can beensured

reinforce-Unsupported sections should be designed in accordancewith Section 2.3 Sufficient longitudinal and lateral steelshould be used for the loads and stresses to be resisted.Uplift loads can be provided for by one or more longitudi-nal bars extending through that portion of the pile subjected

to tensile stresses For pipe or tube piles, dowels welded tothe shell or embedded in the concrete, together with adequate

shear connectors, can be used to transfer the uplift loads from

the structure to the pile

For lateral loads, the pile should be designed and reinforced

to take the loads and stresses involved with consideration

given to the resistance offered by the soil against the pile, the

pile cap, and the foundation walls, as well as the effect of

compressive axial loads

In general, the amount of reinforcement required will be

governed by the loads involved and the design analysis

Ex-cept for uplift loads, it is recommended that not less than four

longitudinal bars be used The extent of reinforcement below

the ground surface depends on the flexural and load

distribu-tion analyses

For auger-grout piles, the addition of a central reinforcing

bar extending at least 10 ft (3 m) into the pile is recommended

This adds toughness to resist accidental bending and tension

forces resulting from other construction activities

2.5.3.5 Stubs in prestressed piles—Structural steel

stubs (or stingers) are sometimes used as extensions from the

tips of prestressed piles Structural steel stubs most

frequent-ly consist of heavy H-pile sections, but other structural

shapes, fabricated crosses, steel rails, and large-diameter

dowels are also used

Stubs can be welded to steel plates, which are in turn

chored to the pile They are, however, most frequently

an-chored by direct embedment of the stub into the body of the

precast pile Design of the stub attachment requires special

attention to ensure proper transfer of the forces between the

prestressed pile and the stub Heavy transverse ties or spiral

reinforcement are needed around the embedded portion of

the stub to provide confinement, and shear studs are

some-times used to aid in bond development Holes through theweb and flanges of the stub (vent holes) may be required topermit the escape of air and water, and thereby help ensureproper concrete placement (Sections 4.5.3.1, 5.6.2, and

5.6.3)

2.5.3.6 Cover for reinforcement—The minimum

rec-ommended clear cover for any pile reinforcement is rized in Table 2.6 for various pile types and exposureconditions

summa-2.5.4 Concrete for CIP and CIS concrete piles—The

de-signer should give consideration to the factors affecting crete placement in CIP and CIS piles when preparingspecifications for this kind of work This includes suchthings as proportioning of the concrete to give a slump in the 4

con-to 6 in (100 con-to 150 mm) range or suitable flow cone valuesfor auger-grout piles and placement methods (Sections 3.1,

3.5, and 5.5)

2.5.5 Rock sockets for drilled-in-piles—The design of

drilled-in-piles requires the determination of an adequaterock socket for the working loads involved The design of therock socket is usually based on the peripheral bond betweenthe concrete filling and the rock If the socket can be thor-oughly cleaned out and inspected, and the concrete can beplaced in the dry, it may be possible to use a combination ofend bearing and bond to develop the required load The com-bined use of end bearing and bond, however, may not be per-mitted by the applicable building code

CHAPTER 3—MATERIALS 3.1—Concrete

3.1.1 Cement—Portland cement should conform to either

ASTM C 150 (Types I, II, III, or V) or ASTM C 595 (Types

IS, IS[MS], P, or IP) Selection of the appropriate tion and cement types for a particular concrete pile projectshould be based on the environment to which the piles are to

specifica-be exposed and the durability requirements given in Chapter 4

of ACI 318-95

The principal consideration in the selection of cement typefor sulfate resistance in ACI 318-95 is the tricalcium alumi-nate (C3A) content For example, concrete piles with moder-ate exposure to sulfate-containing soils or water (soilscontaining 0.1 to 0.2% by weight of water-soluble sulfate[SO4] or water containing 150 to 1500 ppm sulfate) should

be made with cement containing not more than 8%

tricalci-um altricalci-uminate, such as ASTM C 150 Type II cement or erate sulfate-resistant blended cement (MS) Similarly, forsevere sulfate exposure, use ASTM C 150 Type V cement,which contains not more than 5% tricalcium aluminate, andfor very severe sulfate exposure, use ASTM C 150 Type Vcement with a fly ash admixture

mod-Type V cement is not generally available in most sections

of the country In areas where Type V cement is not able, a comparable substitution needs to be specified (for ex-ample, Type II with tricalcium aluminate less than 8% withType F fly ash at approximately 20% by weight, see Section

Precast-reinforced piles—normal exposure * 1.5 (40)

Precast-reinforced piles—normal exposure,

bars No 5 and smaller 1.25 (35)

Precast-reinforced piles—marine exposure † 2.0 (50)

Precast-reinforced piles—normal exposure ‡ 1.5 (40)

Precast-reinforced piles—marine exposure †,‡ 2.0 (50)

* A cover on the spiral of 7/8 in (22 mm) for 10 in (250 mm) diameter piles and 1-3/8

in (35 mm) for 12 in (300 mm) piles have been successfully used for precast piles that

are cast vertically and internally vibrated from the bottom up as the concrete is placed.

† For marine exposures, consider the following section from the Commentary to ACI

318-95 when selecting concrete materials and cover values:

“R7.7.7—Corrosive Environments—When concrete will be exposed to external

sources of chlorides in service, such as deicing salts, brackish water, seawater, or spray

from these sources, concrete must be proportioned to satisfy the special exposure

re-quirements of Chapter 4 These include minimum air content, maximum

water-cemen-titious materials ratio, minimum strength for normal weight and lightweight concrete,

maximum chloride ion in concrete, and cement type Additionally, for corrosion

pro-tection, a minimum concrete cover for reinforcement of 2 in (50 mm) for walls and 2.5

in (65 mm) for other members is recommended For precast concrete manufactured

under plant control conditions, a minimum cover of 1.5 and 2 in (40 and 50 mm),

re-spectively, is recommended.”

‡ For prestressed piles under exposure, the required cover could range from 2 to 3 in.

(50 to 70 mm) For certain types of centrifugally cast prestressed post-tensioned piles,

a cover of 1.5 in (40 mm) has given statisfactory service under 20 years of marine

ex-posure in the Gulf of Mexico (Snow 1983) A 1.5 in (40 mm) cover is recommended

only if such piles are manufactured by a process using no-slump concrete containing a

minimum of 658 lb of cement per yd3 (390 kg.m3) of concrete.